U.S. patent application number 14/733783 was filed with the patent office on 2015-12-10 for patterned transparent conductors and related compositions and manufacturing methods.
The applicant listed for this patent is Iinnova Dynamics, Inc.. Invention is credited to Christopher L. Anderson, James W. Borchert, Ralph E. Korenbrekke, James Kundrat, Andrew Loxley, Sheng Peng, J. Russell Renzas, Vyankat Sindphale, Arjun D. Srinivas, Hichang Yoon.
Application Number | 20150359105 14/733783 |
Document ID | / |
Family ID | 54767509 |
Filed Date | 2015-12-10 |
United States Patent
Application |
20150359105 |
Kind Code |
A1 |
Yoon; Hichang ; et
al. |
December 10, 2015 |
PATTERNED TRANSPARENT CONDUCTORS AND RELATED COMPOSITIONS AND
MANUFACTURING METHODS
Abstract
A manufacturing method of a patterned transparent conductor
includes: (1) providing a transparent conductor including nanowires
formed of a metal; and (2) applying a percolation-inhibition
composition to a portion of the transparent conductor to partially
degrade nanowires included in the portion. The
percolation-inhibition composition includes a complexing agent for
the metal.
Inventors: |
Yoon; Hichang; (Pleasanton,
CA) ; Kundrat; James; (San Francisco, CA) ;
Loxley; Andrew; (San Francisco, CA) ; Srinivas; Arjun
D.; (San Francisco, CA) ; Renzas; J. Russell;
(San Bruno, CA) ; Borchert; James W.; (San
Francisco, CA) ; Peng; Sheng; (San Mateo, CA)
; Sindphale; Vyankat; (San Francisco, CA) ;
Korenbrekke; Ralph E.; (Placitas, NM) ; Anderson;
Christopher L.; (San Francisco, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Iinnova Dynamics, Inc. |
San Francisco |
CA |
US |
|
|
Family ID: |
54767509 |
Appl. No.: |
14/733783 |
Filed: |
June 8, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62009101 |
Jun 6, 2014 |
|
|
|
62012241 |
Jun 13, 2014 |
|
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62157817 |
May 6, 2015 |
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Current U.S.
Class: |
174/268 ; 216/13;
524/555 |
Current CPC
Class: |
C09D 7/65 20180101; H05K
3/061 20130101; C08K 5/17 20130101; H05K 2201/0108 20130101; C09D
5/24 20130101; C09D 7/63 20180101; H05K 3/02 20130101; H05K
2203/0307 20130101; C09D 5/00 20130101; C09D 139/02 20130101; H05K
1/0213 20130101; H05K 2203/1157 20130101; H05K 3/067 20130101; C09D
129/04 20130101; H05K 2203/1142 20130101; C09D 7/40 20180101; H05K
2201/026 20130101; C09D 129/04 20130101; C08K 5/17 20130101 |
International
Class: |
H05K 3/06 20060101
H05K003/06; H05K 1/02 20060101 H05K001/02; C09D 5/00 20060101
C09D005/00; C09D 7/12 20060101 C09D007/12; C09D 129/04 20060101
C09D129/04; C09D 139/02 20060101 C09D139/02 |
Claims
1. A manufacturing method of a patterned transparent conductor,
comprising: providing a transparent conductor including nanowires
formed of a metal; and applying a percolation-inhibition
composition to a portion of the transparent conductor to partially
degrade nanowires included in the portion, wherein the
percolation-inhibition composition includes a complexing agent for
the metal.
2. The manufacturing method of claim 1, wherein applying the
percolation-inhibition composition includes printing the
percolation-inhibition composition over the transparent
conductor.
3. The manufacturing method of claim 2, wherein printing the
percolation-inhibition composition is via screen printing, gravure
printing, or ink-jet printing.
4. The manufacturing method of claim 1, wherein applying the
percolation-inhibition composition includes applying a mask over
the transparent conductor, and applying the percolation-inhibition
composition to the portion through an opening in the mask.
5. The manufacturing method of claim 1, wherein at least one
nanowire included in the portion is severed at one or more
locations along a length of the nanowire.
6. The manufacturing method of claim 1, wherein the complexing
agent is an amine or a polyamine.
7. The manufacturing method of claim 1, wherein the complexing
agent is selected from ammonia, bis(hexamethylene)triamine,
ethylenediamine, diethylenetriamine, octylamine, decylamine,
triethylenetetraamine, N-methylethylenediamine,
N,N'-dimethylethylenediamine, N,N,N'-trimethylethylenediamine,
N,N'-diisopropylethylenediamine, tetraethylpentaamine,
polyethylenimine, lysine, ethanolamine hydrochloride, hydantoin,
and thiourea.
8. The manufacturing method of claim 1, wherein the complexing
agent is an aminated polymer.
9. The manufacturing method of claim 1, wherein the complexing
agent is selected from halides, sulfides, thiocyanates,
polysulfides, and thiosulfates.
10. The manufacturing method of claim 1, wherein the
percolation-inhibition composition further includes a reducing
agent for the metal.
11. The manufacturing method of claim 1, further comprising
activating the percolation-inhibition composition by thermal
treatment.
12. A percolation-inhibition composition for application to
conductive structures formed of a metal, comprising: a complexing
agent for the metal; a polymer binder; and a solvent, wherein the
complexing agent has the formula: ##STR00003## where R.sub.1,
R.sub.2, R.sub.3, and S are independently selected from hydride
groups, alkyl groups, alkenyl groups, alkynyl groups, aryl groups,
poly(alkylene oxide) groups, siloxane groups, and polysiloxane
groups, L is selected from alkylene groups, alkenylene groups,
alkynylene groups, arylene groups, poly(alkylene oxide) groups,
siloxane groups, and polysiloxane groups, A and B are independently
selected from nitrogen, phosphorus, arsenic, antimony, and bismuth,
and n is an integer.gtoreq.0, and where for n>1: L in different
ones of the n units can be the same or different, and are
independently selected from alkylene groups, alkenylene groups,
alkynylene groups, arylene groups, poly(alkylene oxide) groups,
siloxane groups, and polysiloxane groups, S in different ones of
the n units can be the same or different, and are independently
selected from hydride groups, alkyl groups, alkenyl groups, alkynyl
groups, aryl groups, poly(alkylene oxide) groups, siloxane groups,
and polysiloxane groups, and B in different ones of the n units can
be the same or different, and are independently selected from
nitrogen, phosphorus, arsenic, antimony, and bismuth.
13. The percolation-inhibition composition of claim 12, wherein at
least one of A and B is nitrogen.
14. The percolation-inhibition composition of claim 12, wherein the
complexing agent is selected from ammonia,
bis(hexamethylene)triamine, ethylenediamine, diethylenetriamine,
octylamine, decylamine, triethylenetetraamine,
N-methylethylenediamine, N,N'-dimethylethylenediamine,
N,N,N'-trimethylethylenediamine, N,N'-diisopropylethylenediamine,
tetraethylpentaamine, and polyethylenimine.
15. The percolation-inhibition composition of claim 12, wherein the
complexing agent has a boiling point of at least 100.degree. C.
16. The percolation-inhibition composition of claim 12, wherein the
solvent is water, and the polymer binder is a water-soluble polymer
binder.
17. The percolation-inhibition composition of claim 12, wherein the
percolation-inhibition composition is devoid of an oxidizing agent
for the metal.
18. A percolation-inhibition composition for application to
conductive structures formed of a metal, comprising: a complexing
agent for the metal; a reducing agent for the metal; a polymer
binder; and a solvent.
19. The percolation-inhibition composition of claim 18, wherein the
complexing agent is selected from halides, sulfides, thiocyanates,
and polysulfides.
20. The percolation-inhibition composition of claim 18, wherein the
reducing agent is selected from sodium borohydride, citrates,
amines, polyamines, and alcohols.
21. The percolation-inhibition composition of claim 18, wherein the
solvent is water, and the polymer binder is a water-soluble polymer
binder.
22. The percolation-inhibition composition of claim 18, further
comprising at least one of a surfactant, a humectant, and a solid
filler.
23. A patterned transparent conductor comprising: a substrate;
first conductive structures disposed within a first area of the
substrate corresponding to a lower conductance portion; and second
conductive structures disposed within a second area of the
substrate corresponding to a higher conductance portion, wherein a
sheet resistance of the lower conductance portion is at least 100
times a sheet resistance of the higher conductance portion, and
wherein a surface area coverage of the first conductive structures
in the lower conductance portion is less than and is at least 20%
of a surface area coverage of the second conductive structures in
the higher conductance portion.
24. The patterned transparent conductor of claim 23, wherein the
surface area coverage of the first conductive structures in the
lower conductance portion is at least 30% of the surface area
coverage of the second conductive structures in the higher
conductance portion.
25. The patterned transparent conductor of claim 23, wherein the
first conductive structures include first metallic nanowires, the
second conductive structures include second metallic nanowires, and
an average length of the first metallic nanowires is less than an
average length of the second metallic nanowires.
26. The patterned transparent conductor of claim 25, wherein the
average length of the first metallic nanowires is at least 1/100 of
the average length of the second metallic nanowires.
27. The patterned transparent conductor of claim 23, wherein a
percentage by number of nanoparticles among the first conductive
structures in the lower conductance portion is greater than a
percentage by number of nanoparticles among the second conductive
structures in the higher conductance portion.
28. The patterned transparent conductor of claim 23, wherein a
difference in haze values of the higher conductance portion and the
lower conductance portion is no greater than 0.4%, with respect to
a wavelength of 550 nm.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 62/009,101, filed on Jun. 6, 2014, U.S. Provisional
Application No. 62/012,241, filed on Jun. 13, 2014, and U.S.
Provisional Application No. 62/157,817, filed on May 6, 2015, the
disclosures of which are incorporated herein by reference in their
entirety.
TECHNICAL FIELD
[0002] This disclosure relates generally to devices incorporating
conductive structures. More particularly, this disclosure relates
to patterned transparent conductors incorporating conductive
structures to impart functionality such as electrical conductivity
and low visibility patterning.
BACKGROUND
[0003] A transparent conductor permits the transmission of light
while providing a conductive path for an electric current to flow
through a device including the transparent conductor.
Traditionally, a transparent conductor is formed as a coating of a
doped metal oxide, such as tin-doped indium oxide (or ITO), which
is disposed on top of a glass or plastic substrate. ITO coatings
are typically formed through the use of a dry process, such as
through the use of specialized physical vapor deposition (e.g.,
sputtering) or specialized chemical vapor deposition techniques.
The resulting coating can exhibit good electrical conductivity.
However, drawbacks to techniques for forming ITO coatings include
high cost, high process complexity, intensive energy requirements,
high capital expenditures for equipment, and poor productivity.
[0004] For some applications, patterning of a transparent conductor
is desirable to form conductive traces and insulating gaps between
the traces. In the case of ITO coatings, patterning is typically
accomplished via photolithography. However, removing material via
photolithography and related masking and etching processes further
exacerbates the process complexity, the energy requirements, the
capital expenditures, and the poor productivity for patterning
ITO-based transparent conductors. Also, low visibility of patterned
transparent conductors is desirable for certain applications, such
as touch screens. Conventional patterning techniques for ITO
coatings typically result in patterns that are visible to the eye,
which can be undesirable for those applications.
[0005] It is against this background that a need arose to develop
the transparent conductors and related compositions and
manufacturing methods described herein.
SUMMARY
[0006] In some embodiments, a manufacturing method of a patterned
transparent conductor includes: (1) providing a transparent
conductor including nanowires formed of a metal; and (2) applying a
percolation-inhibition composition to a portion of the transparent
conductor to partially degrade nanowires included in the portion.
The percolation-inhibition composition includes a complexing agent
for the metal.
[0007] In additional embodiments, a percolation-inhibition
composition is configured for application to conductive structures
formed of a metal, and includes: (1) a complexing agent for the
metal; (2) a polymer binder; and (3) a solvent. The complexing
agent has the formula:
##STR00001##
[0008] where R.sub.1, R.sub.2, R.sub.3, and S are independently
selected from hydride groups, alkyl groups, alkenyl groups, alkynyl
groups, aryl groups, poly(alkylene oxide) groups, siloxane groups,
and polysiloxane groups, L is selected from alkylene groups,
alkenylene groups, alkynylene groups, arylene groups, poly(alkylene
oxide) groups, siloxane groups, and polysiloxane groups, A and B
are independently selected from nitrogen, phosphorus, arsenic,
antimony, and bismuth, and n is an integer.gtoreq.0, and
[0009] where for n>1: [0010] L in different ones of the n units
can be the same or different, and are independently selected from
alkylene groups, alkenylene groups, alkynylene groups, arylene
groups, poly(alkylene oxide) groups, siloxane groups, and
polysiloxane groups, [0011] S in different ones of the n units can
be the same or different, and are independently selected from
hydride groups, alkyl groups, alkenyl groups, alkynyl groups, aryl
groups, poly(alkylene oxide) groups, siloxane groups, and
polysiloxane groups, and [0012] B in different ones of the n units
can be the same or different, and are independently selected from
nitrogen, phosphorus, arsenic, antimony, and bismuth.
[0013] In additional embodiments, a percolation-inhibition
composition is configured for application to conductive structures
formed of a metal, and includes: (1) a complexing agent for the
metal; (2) a reducing agent for the metal; (3) a polymer binder;
and (4) a solvent.
[0014] In further embodiments, a patterned transparent conductor
includes: (1) a substrate; (2) first conductive structures disposed
within a first area of the substrate corresponding to a lower
conductance portion; and (3) second conductive structures disposed
within a second area of the substrate corresponding to a higher
conductance portion. A sheet resistance of the lower conductance
portion is at least 100 times a sheet resistance of the higher
conductance portion, and a surface area coverage of the first
conductive structures in the lower conductance portion is less than
and is at least 20% of a surface area coverage of the second
conductive structures in the higher conductance portion.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] For a better understanding of the nature and objects of some
embodiments of this disclosure, reference should be made to the
following detailed description taken in conjunction with the
accompanying drawings.
[0016] FIG. 1A and FIG. 1B illustrate examples of transparent
conductors implemented in accordance with embodiments of this
disclosure.
[0017] FIG. 1C illustrates an additional example of a transparent
conductor implemented in accordance with an embodiment of this
disclosure.
[0018] FIG. 2A and FIG. 2B illustrate examples of manufacturing
methods for surface embedding structures into dry compositions,
according to embodiments of this disclosure.
[0019] FIG. 2C illustrates a manufacturing method for surface
embedding structures into a wet composition, according to an
embodiment of this disclosure.
[0020] FIG. 2D illustrates a manufacturing method for incorporating
structures into a wet composition, according to an embodiment of
this disclosure.
[0021] FIG. 3 illustrates an example of modeling a cleaving
mechanism for nanowires, according to an embodiment of this
disclosure.
[0022] FIG. 4 illustrates an example schematic of metallic
nanowires subjected to a chopping or cleaving mechanism or action,
according to an embodiment of this disclosure.
[0023] FIG. 5 illustrates another example schematic of metallic
nanowires subjected to a chopping or cleaving mechanism or action,
according to an embodiment of this disclosure.
[0024] FIG. 6 illustrates another example schematic of metallic
nanowires subjected to a chopping or cleaving mechanism or action,
according to an embodiment of this disclosure.
[0025] FIG. 7A, FIG. 7B, FIG. 7C, FIG. 8A, FIG. 8B, FIG. 8C, FIG.
9A, FIG. 9B, and FIG. 9C illustrate manufacturing methods of
patterned transparent conductors, according to embodiments of this
disclosure.
[0026] FIG. 10A, FIG. 10B, FIG. 10C, FIG. 11A, FIG. 11B, FIG. 11C,
FIG. 12A, FIG. 12B, FIG. 12C, FIG. 13A, FIG. 13B, FIG. 13C, FIG.
14A, FIG. 14B, and FIG. 14C illustrate manufacturing methods of
patterned transparent conductors, according to embodiments of this
disclosure.
[0027] FIG. 15 illustrates an example of a projected capacitive
touch sensor device according to an embodiment of this
disclosure.
[0028] FIG. 16 is a scanning electron microscopy (or SEM) image of
a network of silver nanowires embedded in a substrate, without or
prior to application of an electrical conductivity modifying agent,
according to an embodiment of this disclosure.
[0029] FIG. 17 is a SEM image of a silver nanowire-embedded
substrate subsequent to application of hydrogen peroxide, according
to an embodiment of this disclosure.
[0030] FIG. 18 is a SEM image of a silver nanowire-embedded
substrate subsequent to application of ammonia, according to an
embodiment of this disclosure.
[0031] FIG. 19 is a SEM image of a silver nanowire-embedded
substrate subsequent to application of polyethylenimine, according
to an embodiment of this disclosure.
[0032] FIG. 20 is a SEM image of a silver nanowire-embedded
substrate subsequent to application of bis(hexamethylene)triamine,
according to an embodiment of this disclosure.
[0033] FIG. 21A is a SEM image of a substrate embedded with silver
nanowires containing about 0.6 wt. % of silver chloride, subsequent
to application of bis(hexamethylene)triamine, and FIG. 21B is a SEM
image of a substrate embedded with silver nanowires containing
about 3.41 wt. % of silver chloride, subsequent to application of
bis(hexamethylene)triamine, according to an embodiment of this
disclosure.
[0034] FIG. 22 (top panel) is a SEM image of silver nanowires
treated with 100 vol. % diethylenetriamine (or DETA), and FIG. 22
(bottom panel) is a SEM image of silver nanowires treated with 50
vol. % DETA in isopropyl alcohol (or IPA), according to an
embodiment of this disclosure.
[0035] FIG. 23 is a SEM image of silver nanowires treated with
octylamine, according to an embodiment of this disclosure.
[0036] FIG. 24 is a SEM image of silver nanowires treated with
decylamine, according to an embodiment of this disclosure.
[0037] FIG. 25 is a SEM image of silver nanowires treated with
triethylenetetramine, according to an embodiment of this
disclosure.
[0038] FIG. 26 (top panel) is a SEM image of silver nanowires
treated with N-methylethylenediamine, and FIG. 26 (bottom panel) is
a magnified view of the image, according to an embodiment of this
disclosure.
[0039] FIG. 27 is a SEM image of silver nanowires treated with
N,N'-dimethylethylenediamine, according to an embodiment of this
disclosure.
[0040] FIG. 28 is a SEM image of silver nanowires treated with
N,N'-diisopropylethylenediamine, according to an embodiment of this
disclosure.
[0041] FIG. 29 is a SEM image of silver nanowires treated with
sodium thiosulfate, according to an embodiment of this
disclosure.
[0042] FIG. 30 is a SEM image of untreated silver nanowires, FIG.
31 is a SEM image of silver nanowires treated with
bis(hexamethylene)triamine, and FIG. 32 is a SEM image of silver
nanowires treated with sodium thiosulfate, according to an
embodiment of this disclosure.
[0043] FIG. 33 sets forth results of measurements of lengths of
silver nanowires in a sample of a patterned transparent conductor,
according to an embodiment of this disclosure.
[0044] FIG. 34 is a SEM image of silver nanowires treated with a
percolation-inhibition composition composed of about 5 wt. % of
sodium thiocyanate and 0 wt. % of ascorbic acid, according to an
embodiment of this disclosure.
[0045] FIG. 35 is a SEM image of silver nanowires treated with a
percolation-inhibition composition composed of about 5 wt. % of
sodium thiocyanate and about 0.1 wt. % of ascorbic acid, according
to an embodiment of this disclosure.
[0046] FIG. 36 is a SEM image of silver nanowires treated with a
percolation-inhibition composition composed of about 5 wt. % of
sodium thiocyanate and about 0.5 wt. % of ascorbic acid, according
to an embodiment of this disclosure.
[0047] FIG. 37 is a SEM image of silver nanowires treated with a
percolation-inhibition composition composed of about 5 wt. % of
sodium thiocyanate and about 1 wt. % of ascorbic acid, according to
an embodiment of this disclosure.
[0048] FIG. 38 is a SEM image of silver nanowires treated with a
percolation-inhibition composition composed of about 5 wt. % of
sodium thiocyanate and about 5 wt. % of ascorbic acid, according to
an embodiment of this disclosure.
[0049] FIG. 39 is a SEM image of silver nanowires treated with a
percolation-inhibition composition composed of about 5 wt. % of
sodium thiocyanate and about 10 wt. % of ascorbic acid, according
to an embodiment of this disclosure.
DETAILED DESCRIPTION
Definitions
[0050] The following definitions apply to some of the aspects
described with regard to some embodiments of this disclosure. These
definitions may likewise be expanded upon herein.
[0051] As used herein, the singular terms "a," "an," and "the"
include plural referents unless the context clearly dictates
otherwise. Thus, for example, reference to an object can include
multiple objects unless the context clearly dictates otherwise.
[0052] As used herein, the term "set" refers to a collection of one
or more objects. Thus, for example, a set of objects can include a
single object or multiple objects. Objects of a set can also be
referred to as members of the set. Objects of a set can be the same
or different. In some instances, objects of a set can share one or
more common characteristics.
[0053] As used herein, the term "adjacent" refers to being near or
adjoining. Adjacent objects can be spaced apart from one another or
can be in actual or direct contact with one another. In some
instances, adjacent objects can be connected to one another or can
be formed integrally with one another.
[0054] As used herein, the terms "connect," "connected," and
"connection" refer to an operational coupling or linking. Connected
objects can be directly coupled to one another or can be indirectly
coupled to one another, such as via another set of objects.
[0055] As used herein, the terms "substantially," "substantial,"
and "about" are used to describe and account for small variations.
When used in conjunction with an event or circumstance, the terms
can refer to instances in which the event or circumstance occurs
precisely as well as instances in which the event or circumstance
occurs to a close approximation. When used in conjunction with a
numerical value, the terms can refer to less than or equal to
.+-.10%, such as less than or equal to .+-.5%, less than or equal
to .+-.4%, less than or equal to .+-.3%, less than or equal to
.+-.2%, less than or equal to .+-.1%, less than or equal to
.+-.0.5%, less than or equal to .+-.0.1%, or less than or equal to
.+-.0.05%.
[0056] As used herein, the terms "optional" and "optionally" mean
that the subsequently described event or circumstance may or may
not occur and that the description includes instances where the
event or circumstance occurs and instances in which it does
not.
[0057] As used herein, relative terms, such as "inner," "interior,"
"outer," "exterior," "top," "bottom," "front," "rear," "back,"
"upper," "upwardly," "lower," "downwardly," "vertical,"
"vertically," "lateral," "laterally," "above," and "below," refer
to an orientation of a set of objects with respect to one another,
such as in accordance with the drawings, but do not require a
particular orientation of those objects during manufacturing or
use.
[0058] As used herein, the term "nanometer range" or "nm range"
refers to a range of dimensions from about 1 nanometer ("nm") to
about 1 micrometer ("nm"). The nm range includes the "lower nm
range," which refers to a range of dimensions from about 1 nm to
about 10 nm, the "middle nm range," which refers to a range of
dimensions from about 10 nm to about 100 nm, and the "upper nm
range," which refers to a range of dimensions from about 100 nm to
about 1 .mu.m.
[0059] As used herein, the term "micrometer range" or ".mu.m range"
refers to a range of dimensions from about 1 .mu.m to about 1
millimeter ("mm"). The .mu.m range includes the "lower .mu.m
range," which refers to a range of dimensions from about 1 .mu.m to
about 10 .mu.m, the "middle .mu.m range," which refers to a range
of dimensions from about 10 .mu.m to about 100 .mu.m, and the
"upper .mu.m range," which refers to a range of dimensions from
about 100 .mu.m to about 1 mm.
[0060] As used herein, the term "aspect ratio" refers to a ratio of
a largest dimension or extent of an object and a remaining
dimension or extent of the object (or an average of remaining
dimensions or extents of the object). In some instances, remaining
dimensions of an object can be substantially the same, and an
average of the remaining dimensions can substantially correspond to
either of the remaining dimensions. In some instances, a largest
dimension or extent of an object can be aligned with, or can extend
along, a major axis of the object, while remaining dimensions of
the object can be aligned with, or can extend along, respective
minor axes of the object. For example, an aspect ratio of a
cylinder refers to a ratio of a length of the cylinder and a
cross-sectional diameter of the cylinder. As another example, an
aspect ratio of a spheroid refers to a ratio of dimension along a
major axis of the spheroid and a dimension along a minor axis of
the spheroid.
[0061] As used herein, the term "nano-sized" object refers to an
object that has at least one dimension in the nm range. A
nano-sized object can have any of a wide variety of shapes, and can
be formed of a wide variety of materials. Examples of nano-sized
objects include nanowires, nanotubes, nanoplatelets, nanoparticles,
and other nanostructures.
[0062] As used herein, the term "nanowire" refers to an elongated,
nano-sized object that is substantially solid. Typically, a
nanowire has a lateral dimension (e.g., a cross-sectional dimension
in the form of a width, a diameter, or a width or diameter that
represents an average across orthogonal directions) in the nm
range, a longitudinal dimension (e.g., a length) in the .mu.m
range, and an aspect ratio that is about 3 or greater, such as
about 10 or greater.
[0063] As used herein, the term "nanoplatelet" refers to a
planar-like, nano-sized object that is substantially solid.
[0064] As used herein, the term "nanotube" refers to an elongated,
hollow, nano-sized object. Typically, a nanotube has a lateral
dimension (e.g., a cross-sectional dimension in the form of a
width, an outer diameter, or a width or outer diameter that
represents an average across orthogonal directions) in the nm
range, a longitudinal dimension (e.g., a length) in the .mu.m
range, and an aspect ratio that is about 3 or greater, such as
about 10 or greater.
[0065] As used herein, the term "nanoparticle" refers to a
nano-sized object that is generally or substantially spherical or
spheroidal. Typically, each dimension (e.g., a cross-sectional
dimension in the form of a width, a diameter, or a width or
diameter that represents an average across orthogonal directions)
of a nanoparticle is in the nm range, and the nanoparticle has an
aspect ratio that is less than about 3, such as about 1.
[0066] As used herein, the term "micron-sized" object refers to an
object that has at least one dimension in the .mu.m range.
Typically, each dimension of a micron-sized object is in the .mu.m
range or beyond the .mu.m range. A micron-sized object can have any
of a wide variety of shapes, and can be formed of a wide variety of
materials. Examples of micron-sized objects include microwires,
microtubes, microparticles, and other microstructures.
[0067] As used herein, the term "microwire" refers to an elongated,
micron-sized object that is substantially solid. Typically, a
microwire has a lateral dimension (e.g., a cross-sectional
dimension in the form of a width, a diameter, or a width or
diameter that represents an average across orthogonal directions)
in the .mu.m range and an aspect ratio that is about 3 or greater,
such as about 10 or greater.
[0068] As used herein, the term "microtube" refers to an elongated,
hollow, micron-sized object. Typically, a microtube has a lateral
dimension (e.g., a cross-sectional dimension in the form of a
width, an outer diameter, or a width or outer diameter that
represents an average across orthogonal directions) in the .mu.m
range and an aspect ratio that is about 3 or greater, such as about
10 or greater.
[0069] As used herein, the term "microparticle" refers to a
micron-sized object that is generally or substantially spherical or
spheroidal. Typically, each dimension (e.g., a cross-sectional
dimension in the form of a width, a diameter, or a width or
diameter that represents an average across orthogonal directions)
of a microparticle is in the .mu.m range, and the microparticle has
an aspect ratio that is less than about 3, such as about 1.
[0070] Additionally, concentrations, amounts, ratios, and other
numerical values are sometimes presented herein in a range format.
It is to be understood that such range format is used for
convenience and brevity and should be understood flexibly to
include numerical values explicitly specified as limits of a range,
but also to include all individual numerical values or sub-ranges
encompassed within that range as if each numerical value and
sub-range is explicitly specified. For example, a ratio in the
range of about 1 to about 200 should be understood to include the
explicitly recited limits of about 1 and about 200, but also to
include individual ratios such as about 2, about 3, and about 4,
and sub-ranges such as about 10 to about 50, about 20 to about 100,
and so forth.
Transparent Conductors
[0071] Embodiments of this disclosure relate to conductive
structures, such as metallic nanowires, which are incorporated in
single-layered or multi-layered substrates for use as transparent
conductors or other types of devices. Embodiments of transparent
conductors exhibit improved performance (e.g., higher electrical
and thermal conductivity and higher light transmittance), as well
as cost benefits arising from their composition and manufacturing
methods. In some embodiments, transparent conductors can be
manufactured by a surface embedding process in which conductive
structures are physically embedded into a substrate, while
preserving desired characteristics of the host material (e.g.,
transparency) and imparting additional desired characteristics to
the resulting transparent conductors (e.g., electrical
conductivity). In other embodiments, transparent conductors can be
manufactured by another process, such as an over-coating process.
In some embodiments, transparent conductors can be patterned so as
to include a first set of portions having a first sheet conductance
and a second set of portions having a second sheet conductance
lower than the first sheet conductance. The first set of portions
can correspond to higher sheet conductance (or lower sheet
resistance) portions that function as conductive traces or grids,
while the second set of portions can correspond to lower sheet
conductance (or higher sheet resistance) portions that function as
gaps for electrically isolating the conductive traces. Conductive
structures can be surface-embedded or incorporated in areas of a
substrate corresponding to either, or both, of the portions.
[0072] FIG. 1A and FIG. 1B illustrate examples of transparent
conductors 120 and 126 implemented in accordance with embodiments
of this disclosure. Specifically, FIG. 1A is a schematic of
surface-embedded nanowires 130 that form a percolating network that
is partially exposed and partially buried into a top, embedding
surface 134 of a substrate 132. The embedding surface 134 also can
be a bottom surface of the substrate 132, or multiple surfaces
(e.g., both top and bottom surfaces) on different sides of the
substrate 132 can be embedded with the same or different nanowires.
As illustrated in FIG. 1A, the network of the nanowires 130 is
localized adjacent to the embedding surface 134 and within an
embedded region 138 of the substrate 132, with a remainder of the
substrate 132 largely or substantially devoid of the nanowires 130.
In the illustrated embodiment, the embedded region 138 is
relatively thin (e.g., having a thickness less than or much less
than an overall thickness of the substrate 132, or having a
thickness comparable to a characteristic dimension of the nanowires
130), and, therefore, can be referred to as "planar" or
"planar-like." The transparent conductor 120 can be patterned, such
that FIG. 1A can represent a view of a particular portion of the
patterned transparent conductor 120, such as a higher sheet
conductance portion. FIG. 1A also can represent a view of a lower
sheet conductance portion, in which the network of the nanowires
130 is treated or otherwise processed to result in reduced
electrical conductivity.
[0073] FIG. 1B is a schematic of surface-embedded nanowires 154
that form a percolating network that is partially exposed and
partially buried into a top, embedding surface 156 of a coating or
a top layer 158 that is disposed on top of a bottom layer 160, and
which together constitute a two-layered substrate. As illustrated
in FIG. 1B, the network of the nanowires 154 can be localized
adjacent to the embedding surface 156 and within an embedded region
162 of the coating 158, with a remainder of the coating 158 largely
or substantially devoid of the nanowires 154. It is also
contemplated that the nanowires 154 can be distributed throughout a
larger volume fraction within the coating 158, such as in the case
of a relatively thin coating having a thickness comparable to a
characteristic dimension of the nanowires 154. In the illustrated
embodiment, the embedded region 162 is relatively thin, and,
therefore, can be referred to as "planar" or "planar-like." The
transparent conductor 126 can be patterned, such that FIG. 1B can
represent a view of a particular portion of the patterned
transparent conductor 126, such as a higher sheet conductance
portion. FIG. 1B also can represent a view of a lower sheet
conductance portion, in which the network of the nanowires 154 is
treated or otherwise processed to result in reduced electrical
conductivity.
[0074] FIG. 1C illustrates an additional example of a transparent
conductor 170 implemented in accordance with an embodiment of this
disclosure. Specifically, FIG. 1C is a schematic of nanowires 172
that form a percolating network that is disposed on top of a bottom
layer 174, and is at least partially incorporated in and surrounded
by an over-coating or a top layer 176 that is disposed on top of
the bottom layer 174 and the nanowires 172. As illustrated in FIG.
1C, the network of the nanowires 172 can be localized adjacent to
the bottom layer 174 and within a bottom region of the over-coating
176, with a remainder of the over-coating 176 largely or
substantially devoid of the nanowires 172. It is also contemplated
that the nanowires 172 can be distributed throughout a larger
volume fraction within the over-coating 176, such as in the case of
a relatively thin over-coating having a thickness comparable to a
characteristic dimension of the nanowires 172. In the case of a
relatively thin over-coating, at least some of the nanowires 172
can be partially exposed at a top surface of the over-coating 176.
The transparent conductor 170 can be patterned, such that FIG. 1C
can represent a view of a particular portion of the patterned
transparent conductor 170, such as a higher sheet conductance
portion. FIG. 1C also can represent a view of a lower sheet
conductance portion, in which the network of the nanowires 172 is
treated or otherwise processed to result in reduced electrical
conductivity. It is also contemplated that the nanowires 172 can be
partially embedded into the bottom layer 174 (e.g., similar to the
implementation of FIG. 1A), and then coated with the over-coating
176.
[0075] One aspect of certain transparent conductors described
herein is the provision of a vertical concentration gradient or
profile of conductive structures, such as metallic nanowires,
within at least a portion of a substrate, namely a gradient or
profile along a thickness direction of the substrate. Bulk
incorporation within a substrate or a coating aims to provide a
relatively uniform concentration profile throughout the substrate
or the coating. In contrast, certain transparent conductors
described herein allow for variable, controllable concentration
profile, in accordance with a localization of conductive structures
within an embedded region of at least a portion of a substrate. For
certain implementations, the extent of localization of conductive
structures within a set of embedded regions is such that at least a
majority (by weight, volume, or number density) of the structures
are included within the embedded regions, such as at least about
60% (by weight, volume, or number density) of the structures are so
included, at least about 70% (by weight, volume, or number density)
of the structures are so included, at least about 80% (by weight,
volume, or number density) of the structures are so included, at
least about 90% (by weight, volume, or number density) of the
structures are so included, or at least about 95% (by weight,
volume, or number density) of the structures are so included. For
example, substantially all of the structures can be localized
within the embedded regions, such that a remainder of the substrate
is substantially devoid of the structures. In the case of a
patterned transparent conductor, localization of conductive
structures can vary according to a horizontal concentration
gradient or profile in a substrate, or can vary across multiple
layers included in the patterned transparent conductor.
[0076] Conductive structures, such as the nanowires 130, 154, and
172, can be formed of a variety of electrically conducive or
semiconducting materials, including metals (e.g., silver (or Ag),
nickel (or Ni), palladium (or Pd), platinum (or Pt), copper (or
Cu), and gold (or Au)), metal alloys, semiconductors (e.g., silicon
(or Si), indium phosphide (or InP), and gallium nitride (or GaN)),
metalloids (e.g., tellurium (or Te)), conductive oxides and
chalcogenides that are optionally doped and transparent (e.g.,
metal oxides and chalcogenides that are optionally doped and
transparent such as zinc oxide (or ZnO)), electrically conductive
polymers (e.g., poly(aniline), poly(acetylene), poly(pyrrole),
poly(thiophene), poly(p-phenylene sulfide), poly(p-phenylene
vinylene), poly(3-alkylthiophene), olyindole, poly(pyrene),
poly(carbazole), poly(azulene), poly(azepine), poly(fluorene),
poly(naphthalene), melanins, poly(3,4-ethylenedioxy thiophene) (or
PEDOT), poly(styrenesulfonate) (or PSS), PEDOT-PSS,
PEDOT-poly(methacrylic acid), poly(3-hexylthiophene),
poly(3-octylthiophene), poly(C-61-butyric acid-methyl ester), and
poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene]), and
any combination thereof. In the case of a nanowire formed of a
metal or a metal alloy, a particular example of such a metallic
nanowire is a silver nanowire. Nanowires can have a core-shell
configuration or a core-multi-shell configuration, and can
incorporate a metal halide shell or a metal oxide shell, or other
metal halide or metal oxide portions.
[0077] Although certain embodiments are described in the context of
nanowires, additional embodiments can include other types of
nano-sized structures (or nanostructures) in place of, or in
combination with, nanowires. Further embodiments can be implemented
to include micron-sized structures (or microstructures) in place
of, or in combination with, nanowires. In general, nanostructures
and microstructures can be formed of a variety of materials,
including metals, metal alloys, semiconductors, metalloids,
conductive oxides and chalcogenides that are optionally doped and
transparent, electrically conductive polymers, insulators, and any
combination thereof. To impart electrical conductivity,
nanostructures and microstructures can include an electrically
conductive material, a semiconductor, or a combination thereof
[0078] Examples of electrically conductive materials include metals
(e.g., silver, copper, and gold in the form of silver nanowires,
copper nanowires, and gold nanowires), silver-nickel, silver oxide,
silver with a polymeric capping agent, silver-copper,
copper-nickel, carbon-based materials (e.g., in the form of carbon
nanotubes, graphene, and buckyballs), conductive ceramics (e.g.,
conductive oxides and chalcogenides that are optionally doped and
transparent), electrically conductive polymers, and any combination
thereof
[0079] Examples of semiconductors include semiconducting polymers,
Group IVB elements (e.g., carbon (or C), silicon (or Si), and
germanium (or Ge)), Group IVB-IVB binary alloys (e.g., silicon
carbide (or SiC) and silicon germanium (or SiGe)), Group IIB-VIB
binary alloys (e.g., cadmium selenide (or CdSe), cadmium sulfide
(or CdS), cadmium telluride (or CdTe), zinc oxide (or ZnO), zinc
selenide (or ZnSe), zinc telluride (or ZnTe), and zinc sulfide (or
ZnS)), Group IIB-VIB ternary alloys (e.g., cadmium zinc telluride
(or CdZnTe), mercury cadmium telluride (or HgCdTe), mercury zinc
telluride (or HgZnTe), and mercury zinc selenide (or HgZnSe)),
Group IIIB-VB binary alloys (e.g., aluminum antimonide (or AlSb),
aluminum arsenide (or AlAs), aluminium nitride (or MN), aluminium
phosphide (or AlP), boron nitride (or BN), boron phosphide (or BP),
boron arsenide (or BAs), gallium antimonide (or GaSb), gallium
arsenide (or GaAs), gallium nitride (or GaN), gallium phosphide (or
GaP), indium antimonide (or InSb), indium arsenide (or InAs),
indium nitride (or InN), and indium phosphide (or InP)), Group
IIIB-VB ternary alloys (e.g., aluminium gallium arsenide (or AlGaAs
or Al.sub.xGa.sub.1-xAs), indium gallium arsenide (or InGaAs or
In.sub.xGa.sub.1-xAs), indium gallium phosphide (or InGaP),
aluminium indium arsenide (or AlInAs), aluminium indium antimonide
(or AlInSb), gallium arsenide nitride (or GaAsN), gallium arsenide
phosphide (or GaAsP), aluminium gallium nitride (or AlGaN),
aluminium gallium phosphide (or AlGaP), indium gallium nitride (or
InGaN), indium arsenide antimonide (or InAsSb), and indium gallium
antimonide (or InGaSb)), Group IIIB-VB quaternary alloys (e.g.,
aluminium gallium indium phosphide (or AlGaInP), aluminium gallium
arsenide phosphide (or AlGaAsP), indium gallium arsenide phosphide
(or InGaAsP), aluminium indium arsenide phosphide (or AlInAsP),
aluminium gallium arsenide nitride (or AlGaAsN), indium gallium
arsenide nitride (or InGaAsN), indium aluminium arsenide nitride
(or InAlAsN), and gallium arsenide antimonide nitride (or
GaAsSbN)), and Group IIIB-VB quinary alloys (e.g., gallium indium
nitride arsenide antimonide (or GaInNAsSb) and gallium indium
arsenide antimonide phosphide (or GaInAsSbP)), Group IB-VIIB binary
alloys (e.g., cupruous chloride (or CuCl)), Group IVB-VIB binary
alloys (e.g., lead selenide (or PbSe), lead sulfide (or PbS), lead
telluride (or PbTe), tin sulfide (or SnS), and tin telluride (or
SnTe)), Group IVB-VIB ternary alloys (e.g., lead tin telluride (or
PbSnTe), thallium tin telluride (or Tl.sub.2SnTe.sub.5), and
thallium germanium telluride (or Tl.sub.2GeTe.sub.5)), Group VB-VIB
binary alloys (e.g., bismith telluride (or Bi.sub.2Te.sub.3)),
Group IIB-VB binary alloys (e.g., cadmium phosphide (or
Cd.sub.3P.sub.2), cadmium arsenide (or Cd.sub.3As.sub.2), cadmium
antimonide (or Cd.sub.3Sb.sub.2), zinc phosphide (or
Zn.sub.3P.sub.2), zinc arsenide (or Zn.sub.3As.sub.2), and zinc
antimonide (or Zn.sub.3Sb.sub.2)), and other binary, ternary,
quaternary, or higher order alloys of Group IB (or Group 11)
elements, Group IIB (or Group 12) elements, Group IIIB (or Group
13) elements, Group IVB (or Group 14) elements, Group VB (or Group
15) elements, Group VIB (or Group 16) elements, and Group VIIB (or
Group 17) elements, such as copper indium gallium selenide (or
CIGS), as well as any combination thereof
[0080] Nanostructures and microstructures can include, for example,
metallic or semiconducting nanoparticles, metallic or
semiconducting nanowires (e.g. silver, copper, or zinc), metallic
or semiconducting nanoplatelets, metallic or semiconducting
nanorods, nanotubes (e.g., carbon nanotubes, multi-walled nanotubes
("MWNTs"), single-walled nanotubes ("SWNTs"), double-walled
nanotubes ("DWNTs"), and graphitized or modified nanotubes),
fullerenes, buckyballs, graphene, microparticles, microwires,
microtubes, core-shell nanoparticles or microparticles,
core-multi-shell nanoparticles or microparticles, core-shell
nanowires, and other nano-sized or micron-sized structures having
shapes that are generally or substantially tubular, cubic,
spherical, or pyramidal, and characterized as amorphous, single or
poly-crystalline, tetragonal, hexagonal, trigonal, orthorhombic,
monoclinic, or triclinic, or any combination thereof
[0081] Examples of core-shell nanoparticles and core-shell
nanowires include those with a ferromagnetic core (e.g., iron,
cobalt, nickel, manganese, as well as their oxides and alloys
formed with one or more of these elements), with a shell formed of
a metal, a metal alloy, a metal oxide, carbon, or any combination
thereof (e.g., silver, copper, gold, platinum, a conductive oxide
or chalcogenide, graphene, and other materials listed as suitable
materials herein). A particular example of a core-shell nanowire is
one with a silver core and a gold shell (or a platinum shell or
another type of shell) surrounding the silver core to reduce or
prevent oxidation of the silver core. Another example of a
core-shell nanowire is one with a silver core (or a core formed of
another metal or other electrically conductive material), with a
shell or other coating formed of one or more of the following: (a)
electrically conductive polymers, such as
poly(3,4-ethylenedioxythiophene) (or PEDOT) and polyaniline (or
PANI); (b) conductive oxides, chalcogenides, and ceramics (e.g.,
deposited by sol-gel, chemical vapor deposition, physical vapor
deposition, plasma-enhanced chemical vapor deposition, or chemical
bath deposition); (c) insulators in the form of ultra-thin layers,
such as polymers, SiO.sub.2, BaTiO, and TiO.sub.2; and (d) thin
layers of metals, such as gold, copper, nickel, chromium,
molybdenum, and tungsten. Such coated or core-shell form of
nanowires can be desirable to impart electrical conductivity, while
avoiding or reducing adverse interactions with a host material of a
substrate, such as potential yellowing or other discoloration in
the presence of a metal such as silver, oxidation (e.g., a
silver/gold core/shell nanowires can have substantially lower
oxidation due to the gold shell), and sulfidation (e.g., a
silver/platinum core/shell nanowire can have substantially lower
sulfidation due to the platinum shell).
[0082] For certain implementations, high aspect ratio
nanostructures are desirable, such as in the form of nanowires,
nanotubes, and combinations thereof. For example, desirable
nanostructures include nanotubes formed of carbon or other
materials (e.g., MWNTs, SWNTs, graphitized MWNTs, graphitized
SWNTs, modified MWNTs, modified SWNTs, and polymer-containing
nanotubes), nanowires formed of a metal, a metal oxide, a metal
alloy, or other materials (e.g., silver nanowires, copper
nanowires, zinc oxide nanowires (undoped or doped by, for example,
aluminum, boron, fluorine, and others), tin oxide nanowires
(undoped or doped by, for example, fluorine), cadmium tin oxide
nanowires, ITO nanowires, polymer-containing nanowires, and gold
nanowires), as well as other materials that are electrically
conductive or semiconducting and having a variety of shapes,
whether cylindrical, spherical, pyramidal, or otherwise. Additional
examples of suitable conductive structures include those formed of
activated carbon, graphene, carbon black, or ketjen black, and
nanoparticles formed of a metal, a metal oxide, a metal alloy, or
other materials (e.g., silver nanoparticles, copper nanoparticles,
zinc oxide nanoparticles, ITO nanoparticles, and gold
nanoparticles).
[0083] A host material, within which conductive structures are
surface-embedded or otherwise at least partially incorporated, can
have a variety of shapes and sizes, can be transparent,
translucent, or opaque, can be flexible, bendable, foldable,
stretchable, or rigid, can be electromagnetically opaque or
electromagnetically transparent, and can be electrically
conductive, semiconducting, or insulating. A host material can be
in the form of a layer, a film, or a sheet serving as a substrate,
or can be in the form of a coating or multiple coatings disposed on
top of a bottom layer that together constitute a multi-layered
substrate. A host material can be patterned or unpatterned. For
example, a host material can be formed as a patterned layer that
covers certain areas of a bottom layer while leaving remaining
areas of the bottom layer exposed. As another example, a first host
material can be formed as a first patterned layer overlying certain
areas of a bottom layer, and a second host material (which can
differ from the first host material in some manner) can be formed
as a second patterned layer that covers remaining areas of the
bottom layer. In such manner, the first host material can provide a
first pattern, and the second host material can provide a second
pattern that is an "inverse" of the first pattern. Stated in
another way, the first host material can provide "positive"
portions of a pattern, and the second host material can provide
"negative` portions of the pattern.
[0084] Examples of suitable host materials include organic
materials, inorganic materials, and hybrid organic-inorganic
materials. For example, a host material can include a thermoplastic
polymer, a thermoset polymer, an elastomer, or a copolymer or other
combination thereof, such as selected from polyolefins (e.g.,
polyethylene (or PE), polypropylene (or PP), polybutene, and
polyisobutene), acrylate polymers (e.g., poly(methyl methacrylate)
(or PMMA) type 1 and type 2), polymers based on cyclic olefins
(e.g., cyclic olefin polymers (or COPs) and copolymers (or COCs),
such as available under the trademark ARTON.RTM. and
ZeonorFilm.RTM.), aromatic polymers (e.g., polystyrene),
polycarbonate (or PC), ethylene vinyl acetate (or EVA), ionomers,
polyvinyl butyral (or PVB), polyesters, polysulphones, polyamides,
polyimides, polyurethanes, vinyl polymers (e.g., polyvinyl chloride
(or PVC)), fluoropolymers, polysulfones, polylactic acid, polymers
based on allyl diglycol carbonate, nitrile-based polymers,
acrylonitrile butadiene styrene (or ABS), cellulose triacetate (or
TAC), phenoxy-based polymers, phenylene ether/oxide, a plastisol,
an organosol, a plastarch material, a polyacetal, aromatic
polyamides, polyamide-imide, polyarylether, polyetherimide,
polyarylsulfones, polybutylene, polyketone, polymethylpentene,
polyphenylene, polymers based on styrene maleic anhydride, polymers
based on polyallyl diglycol carbonate monomer, bismaleimide-based
polymers, polyallyl phthalate, thermoplastic polyurethane, high
density polyethylene, low density polyethylene, copolyesters (e.g.,
available under the trademark Tritan.TM.), polyethylene
terephthalate glycol (or PETG), polyethylene terephthalate (or
PET), epoxy, epoxy-containing resin, melamine-based polymers,
silicone and other silicon-containing polymers (e.g., polysilanes
and polysilsesquioxanes), polymers based on acetates,
poly(propylene fumarate), poly(vinylidene
fluoride-trifluoroethylene), poly-3-hydroxybutyrate polyesters,
polycaprolactone, polyglycolic acid (or PGA), polyglycolide,
polyphenylene vinylene, electrically conductive polymers, liquid
crystal polymers, poly(methyl methacrylate) copolymer,
tetrafluoroethylene-based polymers, sulfonated tetrafluoroethylene
copolymers, fluorinated ionomers, polymer corresponding to, or
included in, polymer electrolyte membranes, ethanesulfonyl
fluoride-based polymers, polymers based on
2-[1-[difluoro-[(trifluoroethenyl)oxy]methyl]-1,2,2,2-tetrafluoroethoxy]--
1,1,2,2,-tetrafluoro-, with tetrafluoro ethylene,
tetrafluoroethylene-perfluoro-3,6-dioxa-4-methyl-7-octenesulfonic
acid copolymer, polyisoprene, polyglycolide, polyglycolic acid,
polycaprolactone, polymers based on vinylidene fluoride, polymers
based on trifluoroethylene, poly(vinylidene
fluoride-trifluoroethylene), poly(phenylene vinylene), polymers
based on copper phthalocyanine, cellophane, cuprammonium-based
polymers, rayon, and biopolymers (e.g., cellulose acetate (or CA),
cellulose acetate butyrate (or CAB), cellulose acetate propionate
(or CAP), cellulose propionate (or CP), polymers based on urea,
wood, collagen, keratin, elastin, nitrocellulose, plastarch,
celluloid, bamboo, bio-derived polyethylene, carbodiimide,
cartilage, cellulose nitrate, cellulose, chitin, chitosan,
connective tissue, copper phthalocyanine, cotton cellulose,
elastin, glycosaminoglycans, linen, hyaluronic acid,
nitrocellulose, paper, parchment, plastarch, starch, starch-based
plastics, vinylidene fluoride, and viscose), or any monomer,
copolymer, blend, or other combination thereof. Additional examples
of suitable host materials include ceramics, such as dielectric or
non-conductive ceramics (e.g., SiO.sub.2-based glass;
SiO.sub.x-based glass; TiO.sub.x-based glass; other titanium,
cerium, magnesium analogues of SiO.sub.x-based glass; spin-on
glass; glass formed from sol-gel processing, silane precursor,
siloxane precursor, silicate precursor, tetraethyl orthosilicate,
silane, siloxane, phosphosilicates, spin-on glass, silicates,
sodium silicate, potassium silicate, a glass precursor, a ceramic
precursor, silsesquioxane, metallasilsesquioxanes, polyhedral
oligomeric silsesquioxanes, halosilane, sol-gel, silicon-oxygen
hydrides, silicones, stannoxanes, silathianes, silazanes,
polysilazanes, metallocene, titanocene dichloride, vanadocene
dichloride; and other types of glasses), conductive ceramics (e.g.,
conductive oxides and chalcogenides that are optionally doped and
transparent, such as metal oxides and chalcogenides that are
optionally doped and transparent), and any combination thereof.
Additional examples of suitable host materials include electrically
conductive materials and semiconductors listed above as suitable
materials for conductive structures, such as electrically
conductive polymers like poly(aniline), PEDOT, PSS, PEDOT-PSS, and
so forth. The host material can be, for example, n-doped, p-doped,
or un-doped. Further examples of suitable host materials include
polymer-ceramic composite, polymer-wood composite, polymer-carbon
composite (e.g., formed of ketjen black, activated carbon, carbon
black, graphene, and other forms of carbon), polymer-metal
composite, polymer-oxide, or any combination thereof. The host
material also can incorporate a reducing agent, a corrosion
inhibitor, a moisture barrier material, or other organic or
inorganic chemical agent (e.g., PMMA with ascorbic acid, COP with a
moisture barrier material, or PMMA with a disulfide-type corrosion
inhibitor).
[0085] In some embodiments, confining conductive structures to a
"planar" or "planar-like" embedded region within at least a portion
of a host material can lead to decreased topological disorder of
the structures and increased occurrence of junction formation
between the structures for improved electrical conductivity.
Although an embedded region is sometimes referred as "planar," it
will be understood that such embedded region is typically not
strictly two-dimensional, as the structures themselves are
typically three-dimensional. Rather, "planar" can be used in a
relative sense, with a relatively thin, local concentration of the
structures within a certain region of the host material, and with
the structures largely or substantially absent from a remainder of
the host material. It is noted that the local concentration of
structures can be non-planar in the sense that it can be non-flat.
For example, the structures can be concentrated in a thin region of
the host material that is characterized by curvature with respect
to one or more axes, with the structures largely or substantially
absent from a remainder of the host material. It will also be
understood that an embedded region can be referred as "planar,"
even though such an embedded region can have a thickness that is
greater than (e.g., several times greater than) a characteristic
dimension of the structures. In general, an embedded region can be
located adjacent to a side of a host material, adjacent to a middle
of the host material, or adjacent to any arbitrary location along a
thickness direction of the host material, and multiple embedded
regions can be located adjacent to one another or spaced apart from
one another within the host material. Each embedded region can
include one or more types of conductive structures, and embedded
regions (which are located in the same host material) can include
different types of conductive structures. In the case of a
patterned transparent conductor, multiple embedded regions can be
located across a host material according to a pattern to define a
set of higher sheet conductance portions, a set of lower sheet
conductance portions, or both. In some embodiments, by confining
conductive structures to a set of "planar" embedded regions of a
host material (as opposed to randomly throughout the host
material), a higher electrical conductivity can be achieved for a
given amount of the structures per unit of area. Any conductive
structures not confined to an embedded region represent an excess
amount that can be omitted.
[0086] In some embodiments, transparent conductors can have at
least one conductive structure embedded or otherwise incorporated
in at least a portion of a host material from about 10% (or less,
such as from about 0.1%) by volume of the structure into an
embedding surface and up to about 100% by volume of the structure
into the embedding surface, and can have structures exposed at
varying surface area coverage, such as from about 0.1% exposed
surface area coverage (or less, such as 0% when an embedded region
is entirely below the surface, or when the structures are
completely encapsulated by the host material) up to about 99.9% (or
more) exposed surface area coverage, such as from about 0.1% to
about 10%, about 0.1% to about 8%, or about 0.1% to about 5%
exposed surface area coverage. For example, in terms of a volume of
a conductive structure embedded below the embedding surface
relative to a total volume of the structure, at least one structure
can have an embedded volume percentage (or a population of the
structures can have an average embedded volume percentage) in the
range of about 0% to about 100%, such as from about 10% to about
50%, or from about 50% to about 100%.
[0087] Transparent conductors of some embodiments can have an
embedded region with a thickness greater than a characteristic
dimension of conductive structures used (e.g., for nanowires,
greater than a diameter of an individual nanowire or an average
diameter across the nanowires), with the structures largely or
substantially confined to the embedded region, and with the
thickness less than an overall thickness of a host material. For
example, the thickness of the embedded region can be no greater
than about 95% of the overall thickness of the host material, such
as no greater than about 80%, no greater than about 75%, no greater
than about 50%, no greater than about 40%, no greater than about
30%, no greater than about 20%, no greater than about 10%, or no
greater than about 5% of the overall thickness.
[0088] In some embodiments, conductive structures can be
surface-embedded or otherwise incorporated in at least a portion of
a host material by varying degrees relative to a characteristic
dimension of the structures used (e.g., for nanowires, relative to
a diameter of an individual nanowire or an average diameter across
the nanowires). For example, in terms of a distance of a furthest
embedded point on a structure below an embedding surface, at least
one structure can be embedded to an extent of more than about 100%
of the characteristic dimension, or can be embedded to an extent of
not more than about 100% of the characteristic dimension, such as
at least about 5% or about 10% and up to about 80%, up to about
50%, or up to about 25% of the characteristic dimension. As another
example, a population of the structures, on average, can be
embedded to an extent of more than about 100% of the characteristic
dimension, or can be embedded to an extent of not more than about
100% of the characteristic dimension, such as at least about 5% or
about 10% and up to about 80%, up to about 50%, or up to about 25%
of the characteristic dimension. As will be understood, the extent
to which conductive structures are embedded in a host material can
impact a roughness of an embedding surface, such as when measured
as an extent of variation of heights across the embedding surface
(e.g., a standard deviation relative to an average height). In some
embodiments, a roughness of a surface-embedded substrate is less
than a characteristic dimension of embedded structures.
[0089] In some embodiments, at least one conductive structure can
extend out from an embedding surface of a host material from about
0.1 nm to about 1 cm, such as from about 1 nm to about 100 nm, from
about 1 nm to about 50 nm, from about 50 nm to 100 nm, or from
about 100 nm to about 100 .mu.m. In other embodiments, a population
of structures, on average, can extend out from an embedding surface
of a host material from about 0.1 nm to about 1 cm, such as from
about 1 nm to about 100 nm, from about 1 nm to about 50 nm, from
about 50 nm to 100 nm, or from about 100 nm to about 100 .mu.m. In
other embodiments, substantially all of a surface area of a host
material (e.g., an area of an embedding surface) is covered or
occupied by conductive structures. In other embodiments, up to
about 100% or up to about 75% of the surface area is covered or
occupied by additives, such as up to about 50% of the surface area,
up to about 25% of the surface area, up to about 10%, up to about
5%, up to about than 3% of the surface area, or up to about 1% of
the surface area is covered by structures. Conductive structures
need not extend out from an embedding surface of a host material,
and can be localized entirely below the embedding surface. The
degree of embedding and surface area coverage of conductive
structures in a transparent conductor can be selected in accordance
with a particular application.
[0090] In some embodiments, if nanowires are used, characteristics
that can influence electrical conductivity and other desirable
characteristics include, for example, nanowire concentration,
density, or loading level; surface area coverage; nanowire length;
nanowire diameter; uniformity of the nanowires; material type;
stability of nanowire compositions; wire-wire junction resistance;
host material resistance; nanowire conductivity; crystallinity of
the nanowire; and purity. There can be a preference for nanowires
with a low junction resistance and a low bulk resistance in some
embodiments. For attaining higher electrical conductivity while
maintaining high transparency, smaller diameter, longer length
nanowires can be used (e.g., with relatively high aspect ratios to
facilitate nanowire junction formation and in the range of about 50
to about 2,000, such as from about 100 to about 2,000, from about
50 to about 1,000, from about 100 to about 1,000, or from about 100
to about 800), and metallic nanowires, such as silver, copper, and
gold nanowires, can be used. In other embodiments, if the nanowires
are thin, their bulk conductivity can decrease because of a small
cross-sectional area of the nanowires; therefore, in some
embodiments, larger diameter wires can be selected. Using nanowires
to form nanowire networks, such as silver nanowire networks, can be
desirable for some embodiments. Other metallic nanowires,
non-metallic nanowires, such as ITO and other oxide and
chalcogenide nanowires, also can be used. Nanostructures and
microstructures composed of semiconductors with bandgaps outside
the visible optical spectrum energies (e.g., <1.8 eV and >3.1
eV) or near this range, can be used to create transparent
conductors with high optical transparency in that visible light
will typically not be absorbed by the bandgap energies or by
interfacial traps therein. Various dopants can be used to tune the
conductivity of these aforementioned semiconductors, taking into
account the shifted Fermi levels and bandgap edges via the
Moss-Burstein effect. The nanowires can be largely or substantially
uniform or monodisperse in terms of dimensions (e.g., diameter and
length), such as the same within about 5% (e.g., a standard
deviation relative to an average diameter or length), the same
within about 10%, the same within about 15%, or the same within
about 20%. Purity can be, for example, at least about 50%, at least
about 75%, at least about 85%, at least about 90%, at least about
95%, at least about 99%, at least about 99.9%, or at least about
99.99%. Surface area coverage of nanowires can be, for example, up
to about 100%, less than about 100%, up to about 75%, up to about
50%, up to about 25%, up to about 10%, up to about 5%, up to about
3%, or up to about 1%. Silver nanowires can be particularly
desirable for certain embodiments, since silver oxide, which can
form (or can be formed) on surfaces of the nanowires as a result of
oxidation, is electrically conductive. Also, core-shell nanowires
(e.g., silver core with gold or platinum shell) also can decrease
junction resistance. Nanowires can be solution synthesized via a
number of processes, such as a solution-phase synthesis (e.g., the
polyol process), a vapor-liquid-solid (or VLS) synthesis, an
electrospinning process (e.g., using a polyvinyl-based polymer and
silver nitrate, then annealing in forming gas, and baking), a
suspension process (e.g., chemical etching or nano-melt
retraction), and so forth.
[0091] In some embodiments, if nanotubes are used (whether formed
of carbon, a metal, a metal alloy, a metal oxide, or another
material), characteristics that can influence electrical
conductivity and other desirable characteristics include, for
example, nanotube concentration, density, or loading level; surface
area coverage; nanotube length; nanotube inner diameter; nanotube
outer diameter; whether single-walled or multi-walled nanotubes are
used; uniformity of the nanotubes; material type; and purity. There
can be a preference for nanotubes with a low junction resistance in
some embodiments. For reduced scattering in the context of certain
devices such as displays, nanotubes, such as carbon nanotubes, can
be used to form nanotube networks. Alternatively, or in
combination, smaller diameter nanowires can be used to achieve a
similar reduction in scattering relative to the use of larger
diameter nanotubes. Nanotubes can be largely uniform or
monodisperse in terms of dimensions (e.g., outer diameter, inner
diameter, and length), such as the same within about 5% (e.g., a
standard deviation relative to an average outer/inner diameter or
length), the same within about 10%, the same within about 15%, or
the same within about 20%. Purity can be, for example, at least
about 50%, at least about 75%, at least about 85%, at least about
90%, at least about 95%, at least about 99%, at least about 99.9%,
or at least about 99.99%. Surface area coverage of nanotubes can
be, for example, up to about 100%, less than about 100%, up to
about 75%, up to about 50%, up to about 25%, up to about 10%, up to
about 5%, up to about 3%, or up to about 1%.
[0092] In some embodiments, a combination of different types of
high aspect ratio conductive structures (e.g., nanowires,
nanotubes, or both) can be embedded into at least a portion of a
host material, resulting in a transparent conductor. Specifically,
the combination can include a first population of conductive
structures having a first set of morphological characteristics
(e.g., length (average, median, or mode), diameter (average,
median, or mode), aspect ratio (average, median, or mode), or a
combination thereof) and at least a second population of conductive
structures having a second set of morphological characteristics
that differ in some manner from the first set of morphological
characteristics. Each population of structures can be largely or
substantially uniform or monodisperse in terms of its respective
set of morphological characteristics, such as the same within about
5% (e.g., a standard deviation relative to an average diameter,
length, or aspect ratio), the same within about 10%, the same
within about 15%, or the same within about 20%. The resulting
combination of structures can be bimodal or multimodal. For
example, longer and larger diameter nanowires can promote lower
percolation thresholds, thereby achieving higher transparency with
lower conductive material usage. On the other hand, shorter and
smaller diameter nanowires can promote lower haze and higher
transmission of light through a percolating network. However,
smaller diameter nanowires may have higher Ohmic resistance
compared to larger diameter nanowires of the same material. The use
of a combination of longer and larger diameter nanowires and
shorter and smaller diameter nanowires provides a practical
tradeoff between various factors, including higher transparency
(e.g., a lower percolation threshold from the longer nanowires), a
lower haze (e.g., a lower scattering from the smaller diameter
nanowires), a higher uniformity of coverage for a given sheet
resistance or optical haze (e.g., a larger number of smaller
diameter nanowires may be involved to reach a given sheet
resistance, but if well-dispersed the nanowires can form a more
robust network with fewer large-sized, nanowire-free areas), and
higher conductivity (e.g., a lower resistance from the larger
diameter nanowires) relative to the use of either population of
nanowires alone. By way of analogy and not limitation, the longer
and larger diameter nanowires can act as larger current arteries,
while the shorter and smaller diameter nanowires can act as smaller
current capillaries.
[0093] It should be understood that the number and types of
conductive structures can be varied for a given device or
application. For example, any one, or a combination, of silver
nanowires, copper nanowires, and gold nanowires can be used along
with ITO nanoparticles to yield high optical transparency and high
electrical conductivity. Similar combinations include, for example,
any one, or a combination, of silver nanowires, copper nanowires,
and gold nanowires along with any one or more of ITO nanowires, ZnO
nanowires, ZnO nanoparticles, silver nanoparticles, gold
nanoparticles, SWNTs, MWNTs, fullerene-based materials (e.g.,
carbon nanotubes and buckyballs), and ITO nanoparticles. The use of
ITO nanoparticles, nanowires, or layers of conductive oxides or
ceramics (e.g., ITO, aluminum-doped zinc oxide, or other types of
doped or undoped zinc oxides) can provide additional functionality,
such as by serving as a buffer layer to adjust a work function in
the context of a transparent conductor for use in a solar device, a
thin-film solar device, an organic light emitting diode (or OLED)
display device, an OLED lighting device, or similar device to
provide a conductive path for the flow of an electric current, in
place of, or in combination with, a conductive path provided by
other conductive structures.
[0094] In some embodiments, conductive structures are initially
provided as discrete objects. Upon embedding or incorporation in at
least a portion of a host material, the host material can envelop
or surround the structures such that the structures become aligned
or otherwise arranged within a "planar" or "planar-like" embedded
region. In some embodiments for the case of structures such as
nanowires, nanotubes, microwires, microtubes, or other structures
with an aspect ratio greater than 1, the structures become aligned
such that their lengthwise or longitudinal axes are largely
confined to within a range of angles relative to a horizontal
plane, or another plane corresponding, or parallel, to a plane of
an embedding surface. For example, the structures can be elongated
and can be aligned such that their lengthwise or longest-dimension
axes, on average, are confined to a range from about -45.degree. to
about +45.degree. relative to the horizontal plane, such as from
about -35.degree. to about +35.degree., from about -25.degree. to
about +25.degree., from about -15.degree. to about +15.degree.,
from about -5.degree. to about +5.degree., from about -1.degree. to
about +1.degree., from about -0.1.degree. to about +0.1.degree., or
from about -0.01.degree. to about +0.01.degree.. Stated in another
way, lengthwise axes of the structures can be confined such that
.theta.<SIN.sup.-1(t/L), where L=length of a structure,
t=thickness of the host material, and .theta. is an angle relative
to a horizontal plane corresponding to the embedding surface. In
this example, little or substantially none of the structures can
have their lengthwise or longitudinal axes oriented outside of the
range from about -45.degree. to about +45.degree. relative to the
horizontal plane. Within the embedded region, neighboring
structures can contact one another in some embodiments. Such
contact can be improved using higher aspect ratio structures, while
maintaining a relatively low surface area coverage for desired
transparency. In some embodiments, contact between structures, such
as nanowires, nanoparticles, microwires, and microparticles, can be
increased through pressure (e.g., a calendar press), sintering or
annealing, such as low temperature sintering at temperatures of
about 50.degree. C., about 125.degree. C., about 150.degree. C.,
about 175.degree. C., or about 200.degree. C., or in the range of
about 50.degree. C. to about 125.degree. C., about 100.degree. C.
to about 125.degree. C., about 125.degree. C. to about 150.degree.
C., about 150.degree. C. to about 175.degree. C., or about
175.degree. C. to about 200.degree. C., flash sintering, sintering
through the use of redox reactions to cause deposits onto
structures to grow and fuse the structures together, or any
combination thereof. For example, in the case of silver or gold
structures, silver ions or gold ions can be deposited onto the
structures to cause the structures to fuse with neighboring
structures. High temperature sintering at temperatures at or above
about 200.degree. C. is also contemplated. It is also contemplated
that little or no contact is needed for certain applications and
devices, where charge tunneling or hopping provides sufficient
electrical conductivity in the absence of actual contact, or where
a host material or a coating on top of the host material may itself
be electrically conductive or semiconducting. Such applications and
devices can operate with a sheet resistance up to about 10.sup.6
.OMEGA./sq or more. Individual structures can be separated by
electrical and quantum barriers for electron transfer.
[0095] Transparent conductors described herein can be quite
durable. In some embodiments, such durability is in combination
with rigidity and robustness, and, in other embodiments, such
durability is in combination with the ability to be flexed, rolled,
bent, and folded, amongst other physical actions, with, for
example, no greater than about 50%, no greater than about 40%, no
greater than about 30%, no greater than about 20%, no greater than
about 15%, no greater than about 10%, no greater than about 5%, no
greater than about 3%, or substantially no decrease in
transmittance, and no greater than about 50%, no greater than about
40%, no greater than about 30%, no greater than about 20%, no
greater than about 15%, no greater than about 10%, no greater than
about 5%, no greater than about 3%, or substantially no increase in
resistance (e.g., surface or sheet resistance). In some
embodiments, the transparent conductors can survive a standard test
for adhesion of coatings (e.g., a Scotch Tape Test) used in the
coatings industry and yield substantially no decrease, or no
greater than about 5% decrease, no greater than about 10% decrease,
no greater than about 15% decrease, no greater than about 20%
decrease, no greater than about 30% decrease, no greater than about
40% decrease, or no greater than about 50% decrease in observed
transmittance, and yield substantially no increase, or no greater
than about 5% increase, no greater than about 10% increase, no
greater than about 15% increase, no greater than about 20%
increase, no greater than about 30% increase, no greater than about
40% increase, or no greater than about 50% increase in observed
resistance (e.g., sheet resistance). In some embodiments, the
transparent conductors can also survive rubbing, scratching,
flexing, physical abrasion, thermal cycling (e.g., exposure to
temperatures up to (or at least) about 600.degree. C., up to (or at
least) about 550.degree. C., up to (or at least) about 500.degree.
C., up to (or at least) about 450.degree. C., or up to (or at
least) about 400.degree. C.), chemical exposure, accelerated life
test ("ALT"), and humidity cycling with substantially no decrease,
no greater than about 50% decrease, no greater than about 40%
decrease, no greater than about 30% decrease, no greater than about
20% decrease, no greater than about 15% decrease, no greater than
about 10% decrease, no greater than about 5% decrease, or no
greater than about 3% decrease in observed transmittance, and with
substantially no increase, no greater than about 50% increase, no
greater than about 40% increase, no greater than about 30%
increase, no greater than about 20% increase, no greater than about
15% increase, no greater than about 10% increase, no greater than
about 5% increase, or no greater than about 3% increase in observed
resistance (e.g., sheet resistance). This enhanced durability can
result from embedding or incorporation of conductive structures in
at least a portion of a host material, such that the structures are
physically or chemically held inside the host material by molecular
chains or other components of the host material. In some cases,
flexing or pressing can be observed to increase conductivity.
[0096] Various standard tests can be used to measure durability,
such as in terms of abrasion resistance. One such test, among
others, is ASTM-F735-06 Standard Test Method for Abrasion
Resistance of Transparent Plastics and Coatings Using the
Oscillating Sand Method. Another test that can be used is ASTM
D1044-08 Standard Test Method for Resistance of Transparent
Plastics to Surface Abrasion. Yet another possible standard test is
ASTM D4060-10 Standard Test Method for Abrasion Resistance of
Organic Coatings by the Taber Abraser. Additional standard tests
that can be used include tests for hardness, such as ASTM
D3363-05(2011)e1 Standard Test Method for Film Hardness by Pencil
Test, ASTM E384, ASTM E10, ASTM B277-95 Standard Test Method for
Hardness of Electrical Contact Materials, and ASTM D2583-06
Standard Test Method for Indentation Hardness of Rigid Plastics by
Means of a Barcol Impressor. Further details on these tests are
available from ASTM International of West Conshohocken, Pa. Other
standardized protocols include the ISO 15184, HS K-5600, ECCA-T4-1.
BS 3900-E19, SNV 37113, SIS 184187, NCN 5350, and MIL C 27 227.
[0097] Another set of tests can be used to measure and evaluate
reliability under ALT conditions. Some industry standards include
dry heat (e.g., 85.degree. C./dry), moist heat (e.g., 60.degree.
C./90% RH, or 85.degree. C./85.degree. RH), dry cold (e.g.,
-30.degree. C./dry), and thermal shock (e.g., 80.degree. C.
40.degree. C. cycle for 30 minutes each). These ALT conditions can
be carried out over hours, days, weeks, or months with samples
exposed to those conditions for extended periods of time or number
of cycles. In certain embodiments of the transparent conductors
disclosed herein, the change in at least one of sheet resistance,
transparency, and haze is controlled within .+-.50%, in other cases
within .+-.25%, in other cases within .+-.10%, and in other cases
within .+-.5%, or lower.
[0098] Another aspect of some embodiments of transparent conductors
is that an electrical percolation threshold can be attained using a
lesser amount of conductive structures. Stated in another way,
electrical conductivity can be attained using less electrically
conductive or semiconducting material, thereby saving material and
associated cost and increasing transparency. As will be understood,
an electrical percolation threshold is typically reached when a
sufficient amount of conductive structures is present to allow
percolation of electrical charge from one structure to another
structure, thereby providing a conductive path across at least
portion of a network of structures. In some embodiments, an
electrical percolation threshold can be observed via a change in
slope of a logarithmic plot of resistance versus loading level of
structures. A lesser amount of electrically conductive or
semiconducting material can be used since structures are largely
confined to a "planar" or "planar-like" embedded region in some
embodiments, thereby greatly reducing topological disorder and
resulting in a higher probability of inter-structure (e.g.,
inter-nanowire or inter-nanotube) junction formation. In other
words, because the structures are confined to a thin embedded
region in at least a portion of a host material, as opposed to
dispersed throughout the thickness of the host material, the
probability that the structures will interconnect and form
junctions can be greatly increased. A lesser amount of electrically
conductive or semiconducting material also can be used in
embodiments where a host material is itself electrically conductive
or semiconducting. In some embodiments, an electrical percolation
threshold can be attained at a loading level of structures in the
range of about 0.001 .mu.g/cm.sup.2 to about 100 .mu.g/cm.sup.2 (or
higher), such as from about 0.01 .mu.g/cm.sup.2 to about 100
.mu.g/cm.sup.2, from about 10 .mu.g/cm.sup.2 to about 100
.mu.g/cm.sup.2, from 0.01 .mu.g/cm.sup.2 to about 0.4
.mu.g/cm.sup.2, from about 0.5 .mu.g/cm.sup.2 to about 5
.mu.g/cm.sup.2, or from about 0.8 .mu.g/cm.sup.2 to about 3
.mu.g/cm.sup.2 for certain structures such as silver nanowires.
These loading levels can be varied according to dimensions,
material type, spatial dispersion, and other characteristics of
structures.
[0099] In addition, a lesser amount of conductive structures can be
used (e.g., as evidenced by a thickness of an embedded region) to
achieve a network-to-bulk transition, which is a parameter
representing a transition of a thin layer from exhibiting effective
material properties of a sparse two-dimensional conductive network
to one exhibiting effective properties of a three-dimensional
conductive bulk material. By confining conductive structures to a
"planar" or "planar-like" embedded region, a lower sheet resistance
can be attained at specific levels of transmittance. Furthermore,
in some embodiments, carrier recombination can be reduced due to
the reduction or elimination of interfacial defects associated with
a separate coating or other secondary material into which
conductive structures are included by bulk incorporation.
[0100] To expound further on these advantages, a network of
conductive structures can be characterized by a topological
disorder and by contact resistance. Topologically, above a critical
density of structures and above a critical density of
structure-structure (e.g., nanowire-nanowire, nanotube-nanotube, or
nanotube-nanowire) junctions, electrical current can readily flow
from a source to a drain. A "planar" or "planar-like" network of
structures can reach a network-to-bulk transition with a reduced
thickness, represented in terms of a characteristic dimension of
the structures (e.g., for nanowires, relative to a diameter of an
individual nanowire or an average diameter across the nanowires).
For example, an embedded region can have a thickness up to about 10
times (or more) of the characteristic dimension, such as up to
about 9 times, up to about 8 times, up to about 7 times, up to
about 6 times, up to about 5 times, up to about 4 times, up to
about 3 times, or up to about 2 times the characteristic dimension,
and down to about 0.05, about 0.1, about 0.2, about 0.3, about 0.4,
or about 0.5 times the characteristic dimension, allowing devices
to be thinner while increasing optical transparency and electrical
conductivity. Accordingly, the transparent conductors described
herein provide, in some embodiments, an embedded region with a
thickness up to about n.times.d (in terms of nm) within which are
localized structures having a characteristic dimension of d (in
terms of nm), where n=2, 3, 4, 5, or higher.
[0101] Another advantage of some embodiments of transparent
conductors is that, for a given level of electrical conductivity,
the transparent conductors can yield higher transparency. This is
because less electrically conductive or semiconducting material can
be used to attain that level of electrical conductivity, in view of
the efficient formation of junctions for a given loading level of
conductive structures, in view of the use of a host material that
is itself electrically conductive or semiconducting, or both. As
will be understood, a transmittance of a thin conductive material
(e.g., in the form of a film) can be expressed as a function of its
sheet resistance R.sub..quadrature. and an optical wavelength, as
given by the following approximate relation for a thin film:
T ( .lamda. ) = ( 1 + 188.5 R .cndot. .sigma. Op ( .lamda. )
.sigma. DC ) - 2 ##EQU00001##
where .sigma..sub.Op and .sigma..sub.DC are the optical and DC
conductivities of the material, respectively. In some embodiments,
silver nanowire networks surface-embedded or otherwise incorporated
in flexible transparent substrates can have sheet resistances as
low as about 3.2 .OMEGA./sq or about 0.2 .OMEGA./sq, or even lower.
In other embodiments, transparent conductors can reach up to about
85% (or more) for human vision or photometric-weighted
transmittance T (e.g., from about 350 nm to about 700 nm) and sheet
resistances as low as about 20 .OMEGA./sq (or below). In still
other embodiments, a sheet resistance of .ltoreq.10 .OMEGA./sq at
.gtoreq.85% (e.g., at least about 85%, at least about 90%, or at
least about 95%, and up to about 97%, about 98%, or more) human
vision transmittance can be obtained with the transparent
conductors. It will be understood that transmittance can be
measured relative to other ranges of optical wavelength, such as
transmittance at a given wavelength or range of wavelengths in the
visible range, such as about 550 nm, a solar-flux weighted
transmittance, transmittance at a given wavelength or range of
wavelengths in the infrared range, and transmittance at a given
wavelength or range of wavelengths in the ultraviolet range. It
will also be understood that transmittance can be measured relative
to a bottom layer of a substrate (if present) (e.g., the
transmittance value would not include the transmittance loss from a
bottom layer that is below a top layer that includes
surface-embedded or incorporated conductive structures), or can be
measured relative to air (e.g., the transmittance value would
include the transmittance loss from a bottom layer of a substrate).
Unless otherwise specified herein, transmittance values are
designated relative to a bottom layer of a substrate (if present),
although similar transmittance values (albeit with somewhat higher
values) are also contemplated when measured relative to air. Also,
it will also be understood that transmittance or another optical
characteristic can be measured relative to an over-coating, such as
an optically clear adhesive (if present) (e.g., the transmittance
value would not include the transmittance loss from an over-coating
overlying a substrate that includes surface-embedded or
incorporated conductive structures), or can be measured relative to
air (e.g., the transmittance value would include the transmittance
loss from an over-coating). Unless otherwise specified herein,
values of optical characteristics are designated relative to an
over-coating (if present), although similar values are also
contemplated when measured relative to air. For some embodiments, a
DC-to-optical conductivity ratio of transparent conductors can be
at least about 100, at least about 115, at least about 300, at
least about 400, or at least about 500, and up to about 600, up to
about 800, or more.
[0102] Certain transparent conductors can include nanowires (e.g.,
silver nanowires) of average diameter in the range of about 1 nm to
about 100 nm, about 10 nm to about 80 nm, about 20 nm to about 80
nm, or about 25 nm to about 45 nm, and an average length in the
range of about 50 nm to about 1,000 nm, about 50 nm to about 500
nm, about 100 nm to about 100 nm, about 500 nm to 50 nm, about 5
.mu.m to about 50 nm, about 20 .mu.m to about 150 nm, about 5 .mu.m
to about 35 nm, about 25 .mu.m to about 80 nm, about 25 .mu.m to
about 50 nm, or about 25 .mu.m to about 40 nm. A top of an embedded
region can be located about 0 nm to about 100 .mu.m below a top,
embedding surface of a host material, such as about 0.0001 nm to
about 100 .mu.m below the embedding surface, about 0.01 nm to about
100 .mu.m below the embedding surface, about 0.1 nm to 100 .mu.m
below the embedding surface, about 0.1 nm to about 5 .mu.m below
the embedding surface, about 0.1 nm to about 3 .mu.m below the
embedding surface, about 0.1 nm to about 1 .mu.m below the
embedding surface, or about 0.1 nm to about 500 nm below the
embedding surface. Nanowires embedded or incorporated in a host
material can protrude from an embedding surface from about 0% by
volume and up to about 90%, up to about 95%, or up to about 99% by
volume. For example, in terms of a volume of a nanowire exposed
above the embedding surface relative to a total volume of the
nanowire, at least one nanowire can have an exposed volume
percentage (or a population of the nanowires can have an average
exposed volume percentage) of up to about 1%, up to about 5%, up to
about 20%, up to about 50%, or up to about 75% or about 95%. At a
transmittance of about 85% or greater (e.g., human vision
transmittance or one measured at another range of optical
wavelengths), a sheet resistance can be no greater than about 500
.OMEGA./sq, no greater than about 400 .OMEGA./sq, no greater than
about 350 .OMEGA./sq, no greater than about 300 .OMEGA./sq, no
greater than about 200 .OMEGA./sq, no greater than about 100
.OMEGA./sq, no greater than about 75 .OMEGA./sq, no greater than
about 50 .OMEGA./sq, no greater than about 25 .OMEGA./sq, no
greater than about 20 .OMEGA./sq, no greater than about 15
.OMEGA./sq, no greater than about 10 .OMEGA./sq, and down to about
1 .OMEGA./sq or about 0.1 .OMEGA./sq, or less. At a transmittance
of about 90% or greater, a sheet resistance can be no greater than
about 500 .OMEGA./sq, no greater than about 400 .OMEGA./sq, no
greater than about 350 .OMEGA./sq, no greater than about 300
.OMEGA./sq, no greater than about 200 .OMEGA./sq, no greater than
about 100 .OMEGA./sq, no greater than about 75 .OMEGA./sq, no
greater than about 50 .OMEGA./sq, no greater than about 25
.OMEGA./sq, no greater than about 20 .OMEGA./sq, no greater than
about 15 .OMEGA./sq, no greater than about 10 .OMEGA./sq, and down
to about 1 .OMEGA./sq or less.
[0103] Certain transparent conductors can include nanotubes (e.g.,
either, or both, MWCNT and SWCNT) of average outer diameter in the
range of about 1 nm to about 100 nm, about 1 nm to about 10 nm,
about 10 nm to about 50 nm, about 10 nm to about 80 nm, about 20 nm
to about 80 nm, or about 40 nm to about 60 nm, and an average
length in the range of about 50 nm to about 100 .mu.m, about 100 nm
to about 100 .mu.m, about 500 nm to 50 .mu.m, about 5 .mu.m to
about 50 .mu.m, about 5 .mu.m to about 35 .mu.m, about 25 .mu.m to
about 80 .mu.m, about 25 .mu.m to about 50 .mu.m, or about 25 .mu.m
to about 40 .mu.m. A top of an embedded region can be located about
0 nm to about 100 .mu.m below a top, embedding surface of a host
material, such as about 0.01 nm to about 100 .mu.m below the
embedding surface, about 0.1 nm to 100 .mu.m below the embedding
surface, about 0.1 nm to about 5 .mu.m below the embedding surface,
about 0.1 nm to about 3 .mu.m below the embedding surface, about
0.1 nm to about 1 .mu.m below the embedding surface, or about 0.1
nm to about 500 nm below the embedding surface. Nanotubes embedded
or incorporated in a host material can protrude from an embedding
surface from about 0% by volume and up to about 90%, up to about
95%, or up to about 99% by volume. For example, in terms of a
volume of a nanotube exposed above the embedding surface relative
to a total volume of the nanotube (e.g., as defined relative to an
outer diameter of a nanotube), at least one nanotube can have an
exposed volume percentage (or a population of the nanotubes can
have an average exposed volume percentage) of up to about 1%, up to
about 5%, up to about 20%, up to about 50%, or up to about 75% or
about 95%. At a transmittance of about 85% or greater (e.g., human
vision transmittance or one measured at another range of optical
wavelengths), a sheet resistance can be no greater than about 500
.OMEGA./sq, no greater than about 400 .OMEGA./sq, no greater than
about 350 .OMEGA./sq, no greater than about 300 .OMEGA./sq, no
greater than about 200 .OMEGA./sq, no greater than about 100
.OMEGA./sq, no greater than about 75 .OMEGA./sq, no greater than
about 50 .OMEGA./sq, no greater than about 25 .OMEGA./sq, no
greater than about 20 .OMEGA./sq, no greater than about 15
.OMEGA./sq, no greater than about 10 .OMEGA./sq, and down to about
1 .OMEGA./sq or less. At a transmittance of about 90% or greater, a
sheet resistance can be no greater than about 500 .OMEGA./sq, no
greater than about 400 .OMEGA./sq, no greater than about 350
.OMEGA./sq, no greater than about 300 .OMEGA./sq, no greater than
about 200 .OMEGA./sq, no greater than about 100 .OMEGA./sq, no
greater than about 75 .OMEGA./sq, no greater than about 50
.OMEGA./sq, no greater than about 25 .OMEGA./sq, no greater than
about 20 .OMEGA./sq, no greater than about 15 .OMEGA./sq, no
greater than about 10 .OMEGA./sq, and down to about 1 .OMEGA./sq or
about 0.1 .OMEGA./sq, or less.
[0104] In the case of a patterned transparent conductor, multiple
embedded regions can be located across a single host material or
across multiple host materials according to a pattern. The
characteristics and ranges set forth herein regarding the nature
and extent of surface embedding generally can apply across the
multiple embedded regions, although the particular nature and
extent of surface embedding can vary across the embedded regions to
create a spatially varying contrast in electrical conductivity.
Surface Embedding and Over-Coating Processes
[0105] The transparent conductors described herein can be formed
according to manufacturing methods that can be carried out in a
highly-scalable, rapid, and low-cost fashion, in which conductive
structures are durably incorporated in a wide variety of host
materials. Some embodiments of the manufacturing methods are
surface embedding processes that can be generally classified into
two categories: (1) surface embedding conductive structures into a
dry composition to yield a host material with the surface-embedded
conductive structures; and (2) surface embedding conductive
structures into a wet composition to yield a host material with the
surface-embedded conductive structures. It will be understood that
such classification is for ease of presentation, and that "dry" and
"wet" can be viewed as relative terms (e.g., with varying degrees
of dryness or wetness), and that the manufacturing methods can
apply to a continuum spanned between fully "dry" and fully "wet."
Accordingly, processing conditions and materials described with
respect to one category (e.g., dry composition) can also apply with
respect to another category (e.g., wet composition), and vice
versa. It will also be understood that hybrids or combinations of
the two categories are contemplated, such as where a wet
composition is dried or otherwise converted into a dry composition,
followed by surface embedding of conductive structures into the dry
composition to yield a host material with the surface-embedded
conductive structures. It will further be understood that, although
"dry" and "wet" sometimes may refer to a level of water content or
a level of solvent content, "dry" and "wet" also may refer to
another characteristic of a composition in other instances, such as
a degree of cross-linking or polymerization.
[0106] Attention first turns to FIG. 2A and FIG. 2B, which
illustrate examples of manufacturing methods for surface embedding
structures into dry compositions, according to embodiments of this
disclosure.
[0107] By way of overview, the illustrated embodiments involve the
application of an embedding fluid to allow conductive structures to
be embedded into a dry composition. In general, the embedding fluid
serves to reversibly alter the state of a polymer or other material
included in the dry composition, such as by dissolving, reacting,
softening, solvating, swelling, or any combination thereof, thereby
facilitating embedding of the structures into the dry composition.
For example, the embedding fluid can be specially formulated to act
as an effective solvent for a polymer, while possibly also being
modified with stabilizers (e.g., dispersants) to help suspend the
structures in the embedding fluid. The embedding fluid also can be
specially formulated to reduce or eliminate problems with
solvent/polymer interaction, such as hazing, crazing, and blushing.
The embedding fluid can include a solvent or a solvent mixture that
is optimized to be low-cost, Volatile Organic Compound
("VOC")-free, VOC-exempt or low-VOC, Hazardous Air Pollutant
("HAP")-free, non-ozone depleting substances ("non-ODS"), low
volatility or non-volatile, and low hazard or non-hazardous. As
another example, the dry composition can include a ceramic or a
ceramic precursor in the form of a gel or a semisolid, and
application of the embedding fluid can cause the gel to be swollen
by filling pores with the fluid, by elongation of partially
uncondensed oligomeric or polymeric chains, or both. As a further
example, the dry composition can include a ceramic or a ceramic
precursor in the form of an ionic polymer, such as sodium silicate
or another alkali metal silicate, and application of the embedding
fluid can dissolve at least a portion of the ionic polymer to allow
embedding of the structures. The embedding of the structures is
then followed by hardening or other change in state of the softened
or swelled composition, resulting in a host material having the
structures embedded therein. For example, the softened or swelled
composition can be hardened by exposure to ambient conditions, or
by cooling the softened or swelled composition. In other
embodiments, the softened or swelled composition is hardened by
evaporating or otherwise removing at least a portion of the
embedding fluid (or other liquid or liquid phase that is present),
applying airflow, applying a vacuum, or any combination thereof. In
the case of a ceramic precursor, curing can be carried out after
embedding such that the ceramic precursor is converted into a glass
or another ceramic. Curing can be omitted, depending on the
particular application. Depending on the particular ceramic
precursor (e.g., a silane), more or less heat can be involved to
achieve various degrees of curing or conversion into a fully
reacted or fully formed glass.
[0108] Referring to FIG. 2A, a dry composition 200 can be provided
in the form of a sheet, a film, or other suitable form to serve as
a substrate. The dry composition 200 can correspond to a host
material and, in particular, can include a material previously
listed as suitable host materials. It is also contemplated that the
dry composition 200 can correspond to a host material precursor,
which can be converted into the host material by suitable
processing, such as drying, curing, cross-linking, polymerizing, or
any combination thereof. Next, and referring to FIG. 2A, conductive
structures 202 and an embedding fluid 204 are applied to the dry
composition 200. The structures 202 can be in solution or otherwise
dispersed in the embedding fluid 204, and can be simultaneously
applied to the dry composition 200 via one-step embedding.
Alternatively, the structures 202 can be separately applied to the
dry composition 200 before, during, or after the embedding fluid
204 treats the dry composition 200. Embedding that involves
separate application of the structures 202 and the embedding fluid
204 can be referred as two-step embedding. Subsequently, the
resulting host material 206 has at least some of the structures 202
partially or fully embedded into a surface of the host material
206. Optionally, suitable processing can be carried out to convert
the softened or swelled composition 200 into the host material 206.
During device assembly, the host material 206 with the embedded
structures 202 can be laminated or otherwise connected to adjacent
device layers, or can serve as a substrate onto which adjacent
device layers are formed, laminated, or otherwise applied.
[0109] In the case of a patterned transparent conductor, surface
embedding according to FIG. 2A can be carried out generally
uniformly across the dry composition 200, followed by spatially
selective or varying treatment to yield higher conductance and
lower conductance portions across the host material 206.
Alternatively, or in conjunction, surface embedding according to
FIG. 2A can be carried out in a spatially selective or varying
manner, such as by applying the structures 202 in a spatially
selective or varying manner, by applying the embedding fluid 204 in
a spatially selective or varying manner, or both.
[0110] FIG. 2B is a process flow similar to FIG. 2A, but with a dry
composition 208 provided in the form of a top layer that is
disposed on top of a bottom layer 210, which together constitute or
serve as a substrate. The dry composition 208 can correspond to a
host material, or can correspond to a host material precursor,
which can be converted into the host material by suitable
processing, such as drying, curing, cross-linking, polymerizing, or
any combination thereof. Other characteristics of the dry
composition 208 can be similar to those described above with
reference to FIG. 2A, and are not repeated below. Referring to FIG.
2B, the bottom layer 210 can be transparent or opaque, can be
flexible or rigid, and can be comprised of, for example, a polymer,
an ionomer, a coated polymer film (e.g., a PET film with a PMMA
hardcoat), ethylene vinyl acetate (or EVA), cyclic olefin polymer
(or COP), cyclic olefin copolymer (or COC), polyvinyl butyral (or
PVB), thermoplastic olefin (or TPO), thermoplastic polyurethane (or
TPU), polyethylene (or PE), polyethylene terephthalate (or PET),
polyethylene terephthalate glycol (or PETG), polycarbonate,
polyvinyl chloride (or PVC), polypropylene (or PP), an acrylate
polymer, acrylonitrile butadiene styrene (or ABS), a ceramic, a
glass, silicon, a metal (e.g., stainless steel or aluminum), or any
combination thereof, as well as any other material previously
listed as suitable host materials. The bottom layer 210 can serve
as a temporary layer that is subsequently removed during device
assembly, or can be retained in a resulting device as a layer or
other component of the device. Next, conductive structures 212 and
an embedding fluid 214 are applied to the dry composition 208. The
structures 212 can be in solution or otherwise dispersed in the
embedding fluid 214, and can be simultaneously applied to the dry
composition 208 via one-step embedding. Alternatively, the
structures 212 can be separately applied to the dry composition 208
before, during, or after the embedding fluid 214 treats the dry
composition 208. As noted above, embedding involving the separate
application of the structures 212 and the embedding fluid 214 can
be referred as two-step embedding. Subsequently, the resulting host
material 216 (which is disposed on top of the bottom layer 210) has
at least some of the structures 212 partially or fully embedded
into a surface of the host material 216. Optionally, suitable
processing can be carried out to convert the softened or swelled
composition 208 into the host material 216. During device assembly,
the host material 216 with the embedded structures 212 can be
laminated or otherwise connected to adjacent device layers, or can
serve as a substrate onto which adjacent device layers are formed,
laminated, or otherwise applied.
[0111] In the case of a patterned transparent conductor, surface
embedding according to FIG. 2B can be carried out generally
uniformly across the dry composition 208, followed by spatially
selective or varying treatment to yield higher conductance and
lower conductance portions across the host material 216.
Alternatively, or in conjunction, surface embedding according to
FIG. 2B can be carried out in a spatially selective or varying
manner, such as by disposing or forming the dry composition 208 in
a spatially selective or varying manner over the bottom layer 210,
by applying the structures 212 in a spatially selective or varying
manner across either, or both, of the dry composition 208 and the
bottom layer 210, by applying the embedding fluid 214 in a
spatially selective or varying manner across either, or both, of
the dry composition 208 and the bottom layer 210, or any
combination thereof
[0112] In some embodiments, conductive structures are dispersed in
an embedding fluid, or are dispersed in a carrier fluid and applied
to a dry composition separately or along with the embedding fluid.
Dispersion can be accomplished by mixing, milling, sonicating,
shaking (e.g., wrist action shaking, rotary shaking), vortexing,
vibrating, flowing, chemically modifying the structures' surfaces,
chemically modifying a fluid, increasing a viscosity of the fluid,
adding a dispersing or suspending agent to the fluid, adding a
stabilization agent to the fluid, changing the polarity of the
fluid, changing the hydrogen bonding of the fluid, changing the pH
of the fluid, or otherwise processing the structures to achieve the
desired dispersion. The dispersion can be uniform or non-uniform,
and can be stable or unstable.
[0113] An embedding fluid can include a solvent or a combination of
two or more different solvents. Suitable solvents include organic
solvents selected from polar aprotic organic solvents, polar protic
organic solvents, and non-polar organic solvents. Depending on a
particular polymer included in a dry composition, water or another
inorganic solvent also can be included. Suitable organic solvents
can include from 1-15, 2-15, 3-15, 3-12, 3-10, 4-10, or 5-10 carbon
atoms per molecule. Particular classes of suitable organic solvents
can include ketones, aldehydes, alcohols, esters, ethers, and
arenes. Examples of suitable ketones include cyclohexanone,
4-methyl cyclohexanone, isophorone, methyl isobutyl ketone (or
MIBK), methyl ethyl ketone (or MEK), acetylacetone, and acetone,
among other cyclic or acyclic ketones including from 1-15, 2-15,
3-15, 3-12, 3-10, 4-10, or 5-10 carbon atoms per molecule. An
example of a suitable aldehyde is salicylaldehyde, among other
aromatic or aliphatic aldehydes including from 1-15, 2-15, 3-15,
3-12, 3-10, 4-10, or 5-10 carbon atoms per molecule. It will be
understood that salicylaldehyde includes a hydroxyl group and,
thus, also can be considered an example of a suitable alcohol.
Additional examples of suitable alcohols include o-methoxyphenol,
m-methoxyphenol, p-methoxyphenol, and diacetone alcohol, among
other aromatic or aliphatic alcohols including from 1-15, 2-15,
3-15, 3-12, 3-10, 4-10, or 5-10 carbon atoms per molecule. It will
be understood that methoxyphenol also can be considered an example
of a suitable ether, and diacetone alcohol also can be considered
an example of a suitable ketone. Examples of suitable esters
include propylene glycol methyl ether acetate (or PGMEA), n-butyl
acetate, methyl salicylate, and ethyl lactate, among other cyclic
or acyclic, aliphatic or aromatic esters including from 1-15, 2-15,
3-15, 3-12, 3-10, 4-10, or 5-10 carbon atoms per molecule. It will
be understood that propylene glycol methyl ether acetate also can
be considered another example of a suitable ether, and methyl
salicylate and ethyl lactate also can be considered additional
examples of suitable alcohols. Additional examples of suitable
ethers include 2-methoxy-1,3-dioxolane, tetrahydrofuran, ethylene
glycol monobutyl ether (or EGMBE), diethylene glycol monobutyl
ether, and diethylene glycol monoethyl ether (or DEGMEE), among
other cyclic or acyclic ethers including from 1-15, 2-15, 3-15,
3-12, 3-10, 4-10, or 5-10 carbon atoms per molecule. It will be
understood that ethylene glycol monobutyl ether and diethylene
glycol monoethyl ether also can be considered additional examples
of suitable alcohols. Examples of suitable arenes include toluene,
benzene, ethyl benzene, and xylene, among other monocyclic or
polycylic arenes including from 5-15 or 5-10 carbon atoms per
molecule. Nitroethane and N-methyl pyrrolidone also can be suitable
organic solvents.
[0114] As explained above for some embodiments, conductive
structures can be in solution or otherwise dispersed in a carrier
fluid, and can be applied to a dry composition along with an
embedding fluid. The carrier fluid can be included to provide
functionality other than softening or swelling a polymer or other
material included in the dry composition. Other functionality
provided by the carrier fluid can include one or a combination of
the following:
[0115] (1) Certain coating tools or processes specify a minimum (or
other threshold) coating thickness of fluids that are applied to a
substrate. Inclusion of an excessive amount of an embedding fluid
that interacts with the substrate can result in excessive softening
or swelling of the substrate, and can lead to over-embedding of
conductive structures deep into the substrate below a surface of
the substrate. Inclusion of a certain fraction of a carrier fluid
that is inert towards the substrate allows compliance with the
minimum coating thickness specified by a coating tool or process,
while also controlling an extent of embedding of structures into
the substrate.
[0116] (2) In some embodiments, a capping agent, such as
poly(vinylpyrrolidone) (or PVP), is surface bound or otherwise
associated with certain structures, such as nanowires. In such
embodiments, an embedding fluid can be optimized towards softening
or swelling a substrate, but may lack sufficient compatibility with
the capping agent. Inclusion of a certain fraction of a carrier
fluid that is compatible with the capping agent addresses the lack
of compatibility between the embedding fluid and the capping agent,
such that the capping agent, along with the structures to which the
capping agent is bound, can be stabilized and remain dispersed in a
dispersion.
[0117] A carrier fluid can include a solvent or a combination of
two or more different solvents. In some embodiments, a carrier
fluid is more volatile than an embedding fluid, such that the
carrier fluid is present in a dispersion of conductive structures
as initially applied to a substrate during a coating process, but
evaporates faster than the embedding fluid. In such manner, the
carrier fluid is removed from the substrate at a faster rate than
the embedding fluid, which remains on the substrate for a longer
period of time to soften or swell the substrate and promote
embedding of the structures into the substrate. Suitable solvents
include organic solvents selected from polar aprotic organic
solvents and polar protic organic solvents. A non-polar organic
solvent or water or another inorganic solvent also can be included.
Suitable organic solvents can include from 1-10, 1-9, 1-8, 1-7,
1-6, 1-5, 1-4, 1-3, 1-2, or 2-3 carbon atoms per molecule. A
particular class of suitable organic solvents includes alcohols,
and examples of suitable alcohols include methyl alcohol, ethyl
alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol,
sec-butyl alcohol, isobutyl alcohol, tert-butyl alcohol, n-pentyl
alcohol, neo-pentyl alcohol, and n-hexyl alcohol, among other
aromatic or aliphatic alcohols including from 1-10, 1-9, 1-8, 1-7,
1-6, 1-5, 1-4, 1-3, 1-2, or 2-3 carbon atoms per molecule. In some
embodiments, a carrier fluid includes a combination of two or more
different solvents having different levels of volatility, such as
where the carrier fluid includes at least a first solvent and a
different, second solvent, the first solvent and the second solvent
are different alcohols, the first solvent is selected from
aliphatic alcohols including from 1-3, 1-2, or 2-3 carbon atoms per
molecule, and the second solvent is selected from aliphatic
alcohols including from 4-10, 4-9, 4-8, 4-7, 4-6, or 4-5 carbon
atoms per molecule.
[0118] Control over surface embedding can be achieved through the
proper balancing of the swelling-dispersion-evaporation-application
stages. This balance can be controlled by, for example, a
solvent-host material interaction parameter, sizes of conductive
structures to be embedded, reactivity and volatility of an
embedding fluid, impinging structure momentum or velocity,
temperature, humidity, pressure, and others factors. More
particularly, examples of processing parameters for surface
embedding are listed below for some embodiments of this
disclosure:
Embedding Fluid Selection:
[0119] Solubility parameter relative to a substrate or other host
material (e.g., Hildebrand and Hansen solubility parameters) [0120]
Compatibility of embedding fluid with surface (e.g., matching or
comparison of dielectric constant, partition coefficient, pKa, and
so forth) [0121] Azeotropes, miscibility [0122] Solvent
diffusion/mobility [0123] Viscosity [0124] Evaporation (flash
point, vapor pressure, cooling, and so forth) [0125] Duration of
solvent exposure to substrate or other host material [0126]
Dispersants, surfactants, stabilizers, rheology modifiers [0127]
Solvent (VOC, VOC-exempt, VOC-free, aqueous based)
Substrate or Other Host Material:
[0127] [0128] Solubility parameters (relative to the solvent
formulation) [0129] Crystallinity [0130] Degree of crosslinking
[0131] Molecular weight [0132] Surface energy [0133]
Co-polymers/composite materials [0134] Surface treatment
Type of Structures:
[0134] [0135] Concentration of structures [0136] Geometry of
structures [0137] Surface modification (e.g., ligands, surfactants)
of structures [0138] Stability of structures in the solvent
formulation
Process Operations and Conditions:
[0138] [0139] Deposition Type/Application method (e.g., spraying,
printing, roll coating, gravure coating, slot-die coating,
capillary coating, meniscus coating, cup coating, blade coating,
airbrushing, immersion, dip coating, and so forth) [0140] Duration
of solvent exposure to substrate or other host material [0141]
Wetting, surface tension [0142] Volume of solvent [0143] Surface
(pre)treatment [0144] Humidity [0145] Surface (post)treatment
[0146] Impact/momentum/velocity of structures onto surface (e.g.,
may influence depth or extent of embedding) [0147] Shear applied to
solvent between host material and applicator [0148] Post-processing
conditions (e.g., heating, evaporation, fluid removal, air-drying,
and so forth)
Other Factors:
[0148] [0149] Wetting/surface tension [0150] Capillary forces,
wicking [0151] Amount of solvent applied to the surface [0152]
Duration of solvent exposure to the surface [0153] Surface
(pre)treatment [0154] Stability of formulation [0155] Diffusion of
embedding fluid into surface: thermodynamic and kinetics
considerations
Mitigation of Undesired Effects:
[0155] [0156] Irreversible destruction [0157] Long
swelling/solubility time [0158] Blushing, hazing [0159] Cracking,
crazing [0160] Environmental conditions (e.g., humidity) [0161]
Permanent softening [0162] Wettability/uneven wetting [0163]
Solution stability [0164] Surface Roughness
[0165] Some, or all, of the aforementioned parameters can be
altered or selected to tune a depth or an extent of embedding of
conductive structures into a given host material. For example, a
higher degree of embedding deep into a surface of a host material
can be achieved by increasing a solvency power of an embedding
fluid interacting with the host material, matching closely Hansen
solubility parameters of the embedding fluid-substrate, prolonging
the exposure duration of the embedding fluid in contact with the
host material, increasing an amount of the embedding fluid in
contact with the host material, elevating a temperature of the
system, increasing a momentum of structures impinging onto the host
material, increasing a diffusion of either, or both, of the
embedding fluid and the structures into the host material, or any
combination thereof
[0166] Fluids (e.g., embedding fluids and carrier fluids) can also
include salts, surfactants, stabilizers, and other additives useful
in conferring a particular set of characteristics on the fluids.
Stabilizers can be included based on their ability to at least
partially inhibit agglomeration of structures. Other stabilizers
can be chosen based on their ability to preserve the functionality
of the structures. Butylated hydroxytoluene (or BHT), for instance,
can act as a good stabilizer and as an antioxidant. Other agents
can be used to adjust rheological properties, evaporation rate, and
other characteristics.
[0167] Fluids and structures can be applied so as to be largely
stationary relative to a surface of a dry composition. In other
embodiments, application is carried out with relative movement,
such as by spraying a fluid onto a surface, by conveying a dry
composition through a falling curtain of a fluid, or by conveying a
dry composition through a pool or bath of a fluid. Application of
fluids and structures can be effected by airbrushing, atomizing,
nebulizing, spraying, electrostatic spraying, pouring, rolling,
curtaining, wiping, spin casting, dripping, dipping, painting,
flowing, brushing, immersing, patterning (e.g., stamping,
controlled spraying, controlled ultrasonic spraying, and so forth),
flow coating methods (e.g., slot-die, capillary coating, meniscus
coating, meyer rod, blade coating, cup coating, draw down, and the
like), printing, gravure printing, lithography, screen printing,
flexo printing, offset printing, roll coating, ink-jet printing,
intaglio printing, or any combination thereof. In some embodiments,
structures are propelled, such as by a sprayer, onto a surface,
thereby facilitating embedding by impact with the surface. In other
embodiments, a gradient is applied to a fluid, structures, or both.
Suitable gradients include magnetic and electric fields. The
gradient can be used to apply, disperse, or propel the fluid,
structures, or both, onto a surface. In some embodiments, the
gradient is used to manipulate structures so as to control the
extent of embedding. An applied gradient can be constant or
variable. Gradients can be applied before a dry composition is
softened or swelled, while the dry composition remains softened or
swelled, or after the dry composition is softened or swelled. It is
contemplated that a dry composition can be heated to achieve
softening, and that either, or both, a fluid and structures can be
heated to promote embedding. In some embodiments, embedding of
structures can be achieved primarily or solely through application
of an embedding fluid, without application of gradients or external
pressure. In some embodiments, embedding of structures can be
achieved through application of pressure (e.g., pressure rollers)
in place of, or in conjunction with, an embedding fluid.
[0168] Application of fluids and conductive structures and
embedding of the structures can be spatially controlled to yield
patterns. In some embodiments, spatial control can be achieved with
a physical mask, which can be placed between an applicator and a
surface to block a segment of applied structures from contacting
the surface, resulting in controlled patterning of embedding. In
other embodiments, spatial control can be achieved with a
photomask. A positive or negative photomask can be placed between a
light source and a surface, which can correspond to a photoresist.
Light transmitted through non-opaque parts of the photomask can
selectively affect a solubility of exposed parts of the
photoresist, and resulting spatially controlled soluble regions of
the photoresist can permit controlled embedding. In other
embodiments, spatial control can be achieved through the use of
electric gradients, magnetic gradients, electromagnetic fields,
thermal gradients, pressure or mechanical gradients, surface energy
gradients (e.g., liquid-solid-gas interfaces, adhesion-cohesion
forces, and capillary effects), printing, or any combination
thereof. Spatial control can also be achieved by printing a
material that differs from a host material and in which embedding
does not occur (or is otherwise inhibited).
[0169] As noted above, conductive structures can be dispersed in an
embedding fluid, and applied to a dry composition along with the
embedding fluid via one-step embedding. Structures also can be
applied to a dry composition separately from an embedding fluid via
two-step embedding. In the latter scenario, the structures can be
applied in a wet form, such as by dispersing in a carrier fluid or
by dispersing in the same embedding fluid or a different embedding
fluid. Still in the latter scenario, the structures can be applied
in a dry form, such as in the form of aerosolized powder. It is
also contemplated that the structures can be applied in a quasi-dry
form, such as by dispersing the structures in a carrier fluid that
is volatile, such as methanol, another low boiling point alcohol,
or another low boiling point organic solvent, which substantially
vaporizes prior to impact with a dry composition.
[0170] Attention next turns to FIG. 2C, which illustrates a
manufacturing method for surface embedding conductive structures
222 into a wet composition 218, according to an embodiment of this
disclosure. Referring to FIG. 2C, the wet composition 218 is
applied to a bottom layer 220 in the form of a coating or a top
layer that is disposed on top of the bottom layer 220, which
together constitute or serve as a substrate. The wet composition
218 can correspond to a dissolved form of a host material and, in
particular, can include a dissolved form, a colloidal form, a
nanoparticle form, a sol-form of any material previously listed as
suitable host materials. It is also contemplated that the wet
composition 218 can correspond to a host material precursor, which
can be converted into the host material by suitable processing,
such as drying, curing, cross-linking, polymerizing, sintering,
calcining, or any combination thereof. For example, the wet coating
composition 218 can be a coating or a top layer that is not fully
cured or set, a cross-linkable coating or top layer that is not
fully cross-linked, which can be subsequently cured or cross-linked
using suitable polymerization initiators or cross-linking agents,
or a coating or a top layer of monomers, oligomers, or a
combination of monomers and oligomers, which can be subsequently
polymerized using suitable polymerization initiators or
cross-linking agents. The wet composition 218 also can be
patterned, for instance, with printing methods like screen, reverse
offset gravure, flexo, or ink jetprinting, or another method. In
some embodiments, the wet composition 218 can include a material
with a liquid phase as well as a solid phase, or can include a
material that is at least partially liquid or has properties
resembling those of a liquid, such as a sol, a semisolid, a gel,
and the like. The bottom layer 220 can be transparent or opaque,
can be flexible or rigid, and can be composed of, for example, a
polymer, an ionomer, EVA, PVB, TPO, TPU, PE, PET, PETG, PMMA,
polycarbonate, PVC, PP, an acrylate polymer, ABS, a ceramic, a
glass, silicon, a metal (e.g., stainless steel or aluminum), or any
combination thereof, as well as any other material previously
listed as suitable host materials. The bottom layer 220 can serve
as a temporary layer that is subsequently removed during device
assembly, or can be retained in a resulting device as a layer or
other component of the device.
[0171] Next, according to the option on the left-side of FIG. 2C,
the structures 222 are applied to the wet composition 218 prior to
drying or while it remains in a state that permits embedding of the
structures 222 within the wet composition 218. In some embodiments,
application of the structures 222 is via a flow coating method
(e.g., slot-die, capillary coating, meyer rod, cup coating, draw
down, and the like). Although not illustrated on the left-side, it
is contemplated that an embedding fluid can be simultaneously or
separately applied to the wet composition 218 to facilitate the
embedding of the structures 222. In some embodiments, embedding of
the structures 222 can be achieved through application of pressure
(e.g., pressure rollers) in place of, or in conjunction with, an
embedding fluid. Subsequently, the resulting host material 224 has
at least some of the structures 222 partially or fully embedded
into a surface of the host material 224. Suitable processing can be
carried out to convert the wet composition 218 into the host
material 224. During device assembly, the host material 224 with
the embedded structures 222 can be laminated or otherwise connected
to adjacent device layers, or can serve as a substrate onto which
adjacent device layers are formed, laminated, or otherwise
applied.
[0172] Certain aspects regarding the application of the structures
222 and the embedding of the structures 222 on the left-side of
FIG. 2C can be carried out using similar processing conditions and
materials as described above for FIG. 2A and FIG. 2B, and those
aspects are not repeated below.
[0173] Referring to the option on the right-side of FIG. 2C, the
wet composition 218 can be initially converted into a dry
composition 226 by suitable processing, such as by at least
partially drying, curing, cross-linking, polymerization, or any
combination thereof. Next, the structures 222 and an embedding
fluid 228 can be applied to the dry composition 226. The structures
222 can be in solution or otherwise dispersed in the embedding
fluid 228, and can be simultaneously applied to the dry composition
226 via one-step embedding. Alternatively, the structures 222 can
be separately applied to the dry composition 226 before, during, or
after the embedding fluid 228 treats the dry composition 226. As
noted above, embedding involving the separate application of the
structures 222 can be referred as two-step embedding. Subsequently,
the resulting host material 224 has at least some of the structures
222 partially or fully embedded into the surface of the host
material 224. Optionally, suitable processing can be carried out to
convert the dry composition 226 into the host material 224, such as
by additional drying, curing, cross-linking, polymerization, or any
combination thereof. Any, or all, of the manufacturing stages
illustrated in FIG. 2C can be carried out in the presence of a
vapor environment of a suitable fluid (e.g., an embedding fluid or
other suitable fluid) to facilitate the embedding of the structures
222, to slow drying of the wet composition 218, or both.
[0174] Certain aspects regarding the application of the structures
222 and the embedding fluid 228 and the embedding of the structures
222 on the right-side of FIG. 2C can be carried out using similar
processing conditions and materials as described above for FIG. 2A
and FIG. 2B, and those aspects are not repeated below. In
particular, and in at least certain aspects, the processing
conditions for embedding the structures 222 into the dry
composition 226 on the right-side of FIG. 2C can be viewed as
largely parallel to those used when embedding the structures 212
into the dry composition 208 of FIG. 2B.
[0175] In the case of a patterned transparent conductor, surface
embedding according to FIG. 2C can be carried out generally
uniformly across the wet composition 218 or the dry composition
226, followed by spatially selective or varying treatment to yield
higher conductance and lower conductance portions across the host
material 224. Alternatively, or in conjunction, surface embedding
according to FIG. 2C can be carried out in a spatially selective or
varying manner, such as by disposing or forming the wet composition
218 in a spatially selective or varying manner over the bottom
layer 220, by applying the structures 222 in a spatially selective
or varying manner across either, or both, of the wet composition
218 and the bottom layer 220, by applying the structures 222 in a
spatially selective or varying manner across either, or both, of
the dry composition 226 and the bottom layer 220, by applying the
embedding fluid 228 in a spatially selective or varying manner
across either, or both, of the dry composition 226 and the bottom
layer 220, or any combination thereof.
[0176] Attention next turns to FIG. 2D, which illustrates a
manufacturing method for incorporating conductive structures 242
into a wet composition 238, according to an embodiment of this
disclosure. Referring to FIG. 2D, the structures 242 are applied to
a bottom layer 240, such as in a substantially dry form or
dispersed in a suitable carrier fluid, and then the wet composition
238 is applied to the bottom layer 240 in the form of an
over-coating or a top layer that is disposed on top of the bottom
layer 240 and at least partially surrounding the structures 242.
The wet composition 238 can correspond to a dissolved form of a
host material and, in particular, can include a dissolved form, a
colloidal form, a nanoparticle form, a sol-form of any material
previously listed as suitable host materials. It is also
contemplated that the wet composition 238 can correspond to a host
material precursor, which can be converted into the host material
by suitable processing, such as drying, curing, cross-linking,
polymerizing, sintering, calcining, or any combination thereof. For
example, the wet coating composition 238 can be an over-coating or
a top layer that is not fully cured or set, a cross-linkable
over-coating or top layer that is not fully cross-linked, which can
be subsequently cured or cross-linked using suitable polymerization
initiators or cross-linking agents, or an over-coating or a top
layer of monomers, oligomers, or a combination of monomers and
oligomers, which can be subsequently polymerized using suitable
polymerization initiators or cross-linking agents. The wet
composition 238 also can be patterned, for instance, with printing
methods like screen, reverse offset gravure, flexo, or ink
jetprinting, or another method. In some embodiments, the wet
composition 238 can include a material with a liquid phase as well
as a solid phase, or can include a material that is at least
partially liquid or has properties resembling those of a liquid,
such as a sol, a semisolid, a gel, and the like. The bottom layer
240 can be transparent or opaque, can be flexible or rigid, and can
be composed of, for example, a polymer, an ionomer, EVA, PVB, TPO,
TPU, PE, PET, PETG, PMMA, polycarbonate, PVC, PP, an acrylate
polymer, ABS, a ceramic, a glass, silicon, a metal (e.g., stainless
steel or aluminum), or any combination thereof, as well as any
other material previously listed as suitable host materials. The
bottom layer 240 can serve as a temporary layer that is
subsequently removed during device assembly, or can be retained in
a resulting device as a layer or other component of the device.
[0177] Next, the wet composition 238 is converted into the host
material, which has at least some of the structures 242 partially
or fully incorporated within the host material. Suitable processing
can be carried out to convert the wet composition 238 into the host
material. During device assembly, the host material with the
incorporated structures 242 can be laminated or otherwise connected
to adjacent device layers, or can serve as a substrate onto which
adjacent device layers are formed, laminated, or otherwise
applied.
Patterning of Transparent Conductors
[0178] Patterned transparent conductors can be used in, for
example, touch sensors, liquid crystal display (or LCD) pixel
electrodes, and other electronic and optoelectronic devices.
Adequate electrical isolation between conductive traces is
desirable to isolate electrical signals to achieve spatial
resolution in touch sensing or pixel switching. Adequate
transparency of the transparent conductors is desirable to achieve
higher display brightness, contrast ratio, image quality, and power
consumption efficiency, while adequate electrical conductivity is
desirable to maintain high signal-to-noise ratios, switching
speeds, refresh rates, response time, and uniformity. For
applications where electrical patterning is desirable but optically
(e.g., visible to the human eye) observable patterning is
undesirable, adequate pattern invisibility or low pattern
visibility is desirable. Electrically isolated patterns that are
nearly or substantially indistinguishable by the human eye are
particularly desirable. Patterning methods that largely or
substantially remove conductive material from portions of a
substrate generally are not desirable because portions with
material removed can be visually distinguished by the human eye
from portions without material removal, either under typical room
illumination or under high intensity light illumination, such as
sunlight exposure or exposure to high intensity visible light from
other sources. Additionally, a low-cost, solution-processable
patterning method or composition is desired, such as to provide
compatibility with ink-jet printing, screen printing, or gravure
printing.
[0179] In some embodiments, a patterned transparent conductor can
include higher sheet conductance portions that are laterally
adjacent and spaced apart by lower sheet conductance portions. It
will be understood that "lower conductance" or "lower sheet
conductance" can encompass an insulating nature in an absolute
sense, but need not necessarily refer to such absolute sense.
Rather, "lower conductance" more generally can refer to a portion
that is sufficiently insulating for purposes of electrical
isolation, or can be relative to another portion having a higher
sheet conductance. In some embodiments, an electrical contrast
between the higher and lower conductance portions can be such that
a surface or sheet resistance of the lower conductance portions can
be at least about 2 times a sheet resistance of the higher
conductance portions, such as at least about 5 times, at least
about 10 times, at least about 20 times, at least about 50 times,
at least about 100 times, at least about 500 times, at least about
1,000 times, at least about 10,000 times, or at least about 100,000
times, and up to about 1,000,000 times, up to about 10,000,000
times, or more. In some embodiments, a surface or sheet resistance
of the lower conductance portions can be at least or greater than
about 200 .OMEGA./sq, such as at least about 250 .OMEGA./sq, at
least about 300 .OMEGA./sq, at least about 350 .OMEGA./sq, at least
about 400 .OMEGA./sq, at least about 500 .OMEGA./sq, at least about
1,000 .OMEGA./sq, at least about 10,000 .OMEGA./sq, or at least
about 100,000 .OMEGA./sq, and up to about 1,000,000 .OMEGA./sq, up
to about 10,000,000 .OMEGA./sq, or more, while a surface or sheet
resistance of the higher conductance portions can be no greater
than or less than about 200 .OMEGA./sq, such as no greater than
about 150 .OMEGA./sq, no greater than about 100 .OMEGA./sq, no
greater than about 75 .OMEGA./sq, no greater than about 50
.OMEGA./sq, no greater than about 25 .OMEGA./sq, no greater than
about 20 .OMEGA./sq, no greater than about 15 .OMEGA./sq, or no
greater than about 10 .OMEGA./sq, and down to about 1 .OMEGA./sq,
down to about 0.1 .OMEGA./sq, or less.
[0180] To reduce an optical contrast between higher conductance and
lower conductance portions, optical characteristics of the lower
conductance portions can sufficiently match optical characteristics
of the higher conductance portions. In such manner, the higher and
lower conductance portions can yield low visibility patterning,
while an electrical contrast is maintained between the higher and
lower conductance portions. By sufficiently matching optical
characteristics of the higher and lower conductance portions, these
portions can be rendered substantially visually indistinguishable
or undetectable to the human eye. The extent to which a patterning
of the higher and lower conductance portions is visually
indistinguishable can be evaluated, for example, across a group of
normally sighted human subjects (e.g., in the young to middle adult
age range) and under photopic conditions. In some embodiments, the
patterning of the higher and lower conductance portions can be
deemed substantially visually indistinguishable if the patterning
is undetected by at least about 90% of the human subjects, such as
at least about 93%, at least about 95%, at least about 97%, at
least about 98%, at least about 99%, or more. In some embodiments,
the patterning of the higher and lower conductance portions can be
deemed substantially visually indistinguishable if a luster of the
higher conductance portions and a luster of the lower conductance
portions are deemed to be the same by at least about 90% of the
human subjects, such as at least about 93%, at least about 95%, at
least about 97%, at least about 98%, at least about 99%, or more,
where the luster can be evaluated along a scale of, for example,
adamantine luster, dull luster, greasy luster, metallic luster,
pearly luster, resinous luster, silky luster, submetallic luster,
vitreous luster, and wavy luster.
[0181] In some embodiments, a difference in light transmittance
values (e.g., an absolute difference between transmittance values
each expressed as a percentage) of the higher and lower conductance
portions can be no greater than about 10%, such as no greater than
about 5%, no greater than about 4%, no greater than about 3%, no
greater than about 2%, no greater than about 1%, no greater than
about 0.5%, no greater than about 0.4%, no greater than about 0.3%,
or no greater than about 0.2%, and down to about 0.1%, down to
about 0.01%, down to about 0.001%, or less, where the transmittance
values can be expressed in terms of human vision or
photometric-weighted transmittance, transmittance at a given
wavelength or range of wavelengths in the visible range, such as
about 550 nm, solar-flux weighted transmittance, transmittance at a
given wavelength or range of wavelengths in the infrared range, or
transmittance at a given wavelength or range of wavelengths in the
ultraviolet range. In some embodiments, a difference in haze values
(e.g., transmitted and reflected and expressed as an absolute
difference between haze values each expressed as a percentage) of
the higher and lower conductance portions can be no greater than
about 5%, such as no greater than about 4%, no greater than about
3%, no greater than about 2%, no greater than about 1%, no greater
than about 0.5%, no greater than about 0.4%, no greater than about
0.3%, no greater than about 0.2%, or no greater than 0.1%, and down
to about 0.05%, down to about 0.01%, down to about 0.001%, or less,
where the haze values can be expressed as human vision or
photometric-weighted haze, haze at a given wavelength or range of
wavelengths in the visible range, such as about 550 nm, solar-flux
weighted haze, haze at a given wavelength or range of wavelengths
in the infrared range, or haze at a given wavelength or range of
wavelengths in the ultraviolet range. In some embodiments, a
difference in light absorbance values (e.g., an absolute difference
between absorbance values each expressed as a percentage) of the
higher and lower conductance portions can be no greater than about
10%, such as no greater than about 5%, no greater than about 4%, no
greater than about 3%, no greater than about 2%, no greater than
about 1%, no greater than about 0.5%, no greater than about 0.4%,
no greater than about 0.3%, or no greater than about 0.2%, and down
to about 0.1%, down to about 0.01%, down to about 0.001%, or less,
where the absorbance values can be expressed as human vision or
photometric-weighted absorbance, absorbance at a given wavelength
or range of wavelengths in the visible range, such as about 550 nm,
solar-flux weighted absorbance, absorbance at a given wavelength or
range of wavelengths in the infrared range, or absorbance at a
given wavelength or range of wavelengths in the ultraviolet range.
In some embodiments, a difference in reflectance values (e.g., an
absolute difference between diffuse reflectance values each
expressed as a percentage) of the higher and lower conductance
portions can be no greater than about 10%, such as no greater than
about 5%, no greater than about 4%, no greater than about 3%, no
greater than about 2%, no greater than about 1%, no greater than
about 0.5%, no greater than about 0.4%, no greater than about 0.3%,
or no greater than about 0.2%, and down to about 0.1%, down to
about 0.01%, down to about 0.001%, or less, where the reflectance
values can be expressed as human vision or photometric-weighted
reflectance, reflectance at a given wavelength or range of
wavelengths in the visible range, such as about 550 nm, solar-flux
weighted reflectance, reflectance at a given wavelength or range of
wavelengths in the infrared range, or reflectance at a given
wavelength or range of wavelengths in the ultraviolet range. In
some embodiments, a difference between corresponding pairs of color
stimulus values of the higher and lower conductance portions (e.g.,
an absolute difference between a corresponding pair of color
stimulus values expressed as a percentage relative to either of the
color stimulus values) can be no greater than about 10%, such as no
greater than about 5%, no greater than about 4%, no greater than
about 3%, no greater than about 2%, no greater than about 1%, no
greater than about 0.5%, no greater than about 0.4%, no greater
than about 0.3%, or no greater than about 0.2%, and down to about
0.1%, down to about 0.01%, down to about 0.001%, or less, where the
color stimulus values can be parameters in a suitable color space,
such as the International Commission on Illumination (or CIE) 1931
RGB and CIE 1931 XYZ color spaces.
[0182] In some embodiments, patterning of transparent conductors
can be carried out by applying a spatially selective or varying
treatment to inhibit or disrupt percolation over portion or potions
where electrical conductivity is not desired, such as by inhibiting
the formation of a percolating network, inhibiting electrical
conductivity of the percolating network, or rendering a percolating
network non-percolating by some mechanism or action, such as
breaking or severing individual conductive structures of a
pre-formed percolating network to render the network
non-percolating, or any combination thereof. It should be
understood that inhibition of percolation can encompass full or
substantially full inhibition of percolation as well as partial
inhibition of percolation (or a reduction in percolation). Thus,
for example, a percolation-inhibition treatment or composition as
characterized herein also can encompass a percolation-reducing
treatment or composition. Also, a percolation-inhibition treatment
or composition as characterized herein also can encompass an
electrical conductivity modifying treatment or composition (e.g., a
paste or an ink), in which one or more electrical conductivity
modifying agents are applied to inhibit or disrupt percolation.
[0183] In physical inhibition of percolation, conductive structures
embedded or incorporated in portions intended to become lower
conductance portions are treated to inhibit effective physical
contact with one another to form a percolating network, whereas
conductive structures embedded or incorporated in higher
conductance portions can contact one another, resulting in a
percolating network of the conductive structures in the higher
conductance portions. Physical inhibition of percolation can
involve introducing spacer agents between the structures in the
portions intended to become lower conductance portions to inhibit
effective contact and electron conduction across junctions. In
chemical inhibition of percolation, conductive structures embedded
or incorporated in portions intended to become lower conductance
portions are exposed to a chemical agent or otherwise chemically
treated to inhibit effective contact with one another to form a
percolating network, whereas conductive structures embedded or
incorporated in higher conductance portions can contact one
another, resulting in a percolating network in the higher
conductance portions. Chemical inhibition of percolation can
involve introducing chemical agents that chemically bind to, or
surface functionalize, or react with, the structures in the lower
conductance portions to inhibit effective contact and electron
conduction across junctions. In inhibition of percolation through
degradation, conductive structures embedded or incorporated in
portions intended to become lower conductance portions are exposed
to a chemical agent or otherwise chemically treated to inhibit or
inactivate electron conduction across different structures.
Inhibition of percolation through degradation can involve degrading
junctions between conductive structures, degrading the structures
themselves, such as by dissolving or fragmenting the structures or
converting the structures into structures with higher resistivity,
or both. It will be understood that the classification of
"physical," "chemical," and "degradation" manners of inhibiting
percolation is for ease of presentation, and that certain
treatments can inhibit percolation through a combination of two or
more of "physical," "chemical," and "degradation" manners of
inhibiting percolation. Inhibition of percolation also can be
accomplished through interaction between an electrical conductivity
modifying agent with a component of a percolating network of
conductive structures other than the structures themselves, to
reduce a conductivity of the network.
[0184] In the case of physical inhibition of percolation, suitable
spacer agents can be nano-sized or micron-sized, and can be formed
of, or can include, insulating materials, such as ceramics (e.g.,
in the form of nanoparticles or other nano-sized objects formed of
metal and non-metal oxides and chalcogenides, such as fumed silica
or other forms of silica, and titanium dioxide) and organic
materials (e.g., in the form of molecules, monomers, oligomers, and
low molecular weight polymers). One or more spacer agents can be
dispersed in a suitable composition, which can include a thickener
(or a viscosity modifier) and a solvent or other carrier fluid, and
the composition can be applied in a substantially uniform manner or
in a spatially selective or varying manner. In some embodiments,
the composition also can include an embedding fluid to promote
surface embedding of the spacer agents, such that the spacer agents
are at least partially embedded into a host material, and at least
some of the spacer agents are located between conductive structures
in the host material to inhibit effective contact and electron
conduction across junctions. A relatively small size of the spacer
agents can promote their embedding into the host material and
localization of at least some of the spacer agents in between
structures. The composition also can include an anti-oxidant to
protect the spacer agents during storage.
[0185] For example, nanoparticles or other nano-sized objects
formed of an insulating material can be suitable spacer agents. In
the case of nanoparticles or other nano-sized objects formed of
titanium dioxide, the nanoparticles can serve a dual function of
physically spacing apart structures as well as a degradation
function, such as by photo-catalyzing the conversion of water into
oxygen that can oxidize surfaces of the structures. As another
example, suitable spacer agents can include one or more of organic
molecules, organic monomers, organic oligomers, and low molecular
weight organic polymers (e.g., having a number or a weight average
molecular weight of about 20,000 or less, about 10,000 or less,
about 5,000 or less, or about 1,000 or less) having substantially
the same or a similar chemical composition as a host material in
which structures are embedded or incorporated, having substantially
the same or a similar solubility parameter as the host material, or
both. Inorganic analogs of organic molecules, organic monomers,
organic oligomers, and low molecular weight organic polymers also
can be used as spacer agents. Monomers, oligomers, and polymers can
be ultraviolet-curable or polymerizable, and examples of polymers
and associated monomers and oligomers include those previously
listed as suitable host materials. Starches and other
polysaccharides also can be suitable spacer agents. Further
examples of suitable spacer agents include foaming agents that can
yield gas bubbles, and materials that can expand when heated or
otherwise energized.
[0186] In the case of chemical inhibition of percolation, suitable
chemical agents can be sub-nano-sized, nano-sized, or micron-sized,
and can be in the form of molecules, monomers, oligomers, and low
molecular weight polymers that are terminated, derivatized, or
substituted with one or more types of functional groups having an
affinity with, or are capable of forming a chemical bond with,
conductive structures. One or more chemical agents can be dispersed
in a suitable composition, which can include a thickener (or a
viscosity modifier) and a solvent or other carrier fluid, and the
composition can be applied in a substantially uniform manner or in
a spatially selective or varying manner. In some embodiments, the
composition also can include an embedding fluid to promote surface
embedding of the chemical agents, such that the chemical agents are
at least partially embedded into a host material, and at least some
of the chemical agents are chemical bound to, or surface
functionalize, conductive structures in the host material to
inhibit effective contact and electron conduction across junctions.
A relatively small size of the chemical agents can promote their
embedding into the host material and localization of at least some
of the chemical agents surrounding the conductive structures. The
composition also can include an anti-oxidant to protect the
chemical agents during storage, as well as anti-colorants or
anti-yellowing agents to protect against possible discoloration
resulting from the chemical agents.
[0187] Examples of chemical bonds include covalent, ionic, and
coordination bonds, and examples of suitable functional groups
include:
[0188] (1) thiol group, which refers to --SH;
[0189] (2) amino group, which refers to --NH.sub.2;
[0190] (3) N-substituted amino group, which refers to an amino
group that has a set of its hydrogen atoms replaced by a set of
substituent groups. Examples of N-substituted amino groups include
--NRR', where R and R' are selected from hydride groups, alkyl
groups, alkenyl groups, alkynyl groups, and aryl groups, and at
least one of R and R' is not a hydride group;
[0191] (4) hydroxyl group, which refers to --OH;
[0192] (5) cyano group, which refers to --CN;
[0193] (6) nitro group, which refers to --NO.sub.2;
[0194] (7) amide group, which refers to --(C.dbd.O)NH.sub.2;
[0195] (8) N-substituted amide group, which refers to an amide
group that has a set of its hydrogen atoms replaced by a set of
substituent groups. Examples of N-substituted amide groups include
--(C.dbd.O)NRR', where R and R' are selected from hydride groups,
alkyl groups, alkenyl groups, alkynyl groups, and aryl groups, and
at least one of R and R' is not a hydride group;
[0196] (9) carboxy group, which refers to --(C.dbd.O)OH;
[0197] (10) urea group, which refers to --NH(C.dbd.O)NH.sub.2;
[0198] (11) ether group, which refers to --O--;
[0199] (12) functional groups that act as electron donors (e.g.,
Lewis bases) and electron acceptors (e.g., Lewis acids);
[0200] (13) phosphorus-containing groups, such as phosphines;
[0201] (14) carbonyl group, which refers to --(C.dbd.O)--; and
[0202] (15) combinations of two or more of the foregoing.
[0203] For example, suitable chemical agents can include one or
more of thiol-terminated small molecules, oligomers, or polymers;
surfactants; molecular ligands (e.g., crown ethers); and oligomers
and polymers that include electron donating functional groups
(e.g., poly(ethylene oxide)). In the case of chemical agents that
are terminated, derivatized, or substituted with thiol groups, the
chemical agents can serve a dual function of surface
functionalizing conductive structures to physically space apart the
structures as well as a degradation function, such as by
sulfidation of surfaces of the structures, such as promoting the
formation of silver sulfide in the case of silver nanowires.
Examples of suitable thiol-containing chemical agents include those
having the formula: R--SH where R is an alkyl, alkenyl, alkynyl, or
aryl group, a polysiloxane group, or a derivative thereof. Examples
of suitable phosphorus-containing chemical agents include those
having the formula: P(R)(R')(R'') where P is phosphorus, and R, R'
and R'' are independently selected from hydride, alkyl, alkenyl,
alkynyl, aryl, and polysiloxane groups, or derivatives thereof. For
example, a suitable phosphorus-containing chemical agent is
triphenyl phosphine.
[0204] Suitable chemical agents can have substantially the same or
a similar chemical composition as a host material in which
conductive structures are embedded or incorporated, can have
substantially the same or a similar solubility parameter as the
host material, or both. Inorganic analogs of organic molecules,
organic monomers, organic oligomers, and low molecular weight
organic polymers also can be used as chemical agents. Monomers,
oligomers, and polymers can be ultraviolet-curable or
polymerizable, and examples of polymers and associated monomers and
oligomers include those previously listed as suitable host
materials that include or are terminated, derivatized, or
substituted with suitable functional groups.
[0205] Inhibition of percolation through degradation can be
accomplished by chemical agents or other treatments that chemically
react with, degrade, or otherwise modify surfaces of conductive
structures to render the surfaces less electrically conductive, or
damage, break, fragment, etch, or dissolve the structures
(selectively, preferentially, partially, or wholly). To attain low
visibility patterning, inhibition of percolation through
degradation can involve a balance between sufficient degradation to
reduce an electrical conductivity of a percolating network in lower
conductance portions without excessive degradation that would
result in undesirable optical contrast between the lower
conductance portions and higher conductance portions.
[0206] In some embodiments for the case of nanowires or other high
aspect ratio nanostructures, inhibition of percolation through
degradation can attain such a balance through a chopping or
cleaving mechanism or action, in which nanowires are severed at one
or more locations along their lengths to result in shorter or lower
aspect ratio nanowires or other nanostructures. FIG. 3 illustrates
an example of modeling a cleaving mechanism, in which a change in
haze and a change in sheet resistance (in terms of .OMEGA./sq or
OPS) are plotted versus a number of breaks introduced per nanowire
in an initially percolating network of nanowires. Electrical
percolation depends on nanowire length. Above a percolation
threshold, the network is electrically conductive, while the
network is insulating or non-percolating below the percolation
threshold. Shorter nanowires typically have a higher percolation
threshold, in terms of a surface area coverage or a loading level
of the nanowires in the network. As shown in FIG. 3, the cleaving
mechanism can increase a sheet resistance of the network of
nanowires by introducing breaks in the nanowires and thereby
decreasing a length of the nanowires. The cleaving mechanism causes
a percolation threshold to rise to a level equal to or above a
surface area coverage or a loading level of the nanowires, at which
point the sheet resistance increases sharply. A material of the
nanowires is removed from the breaks, thereby reducing a surface
area coverage or a loading level of the nanowires and reducing haze
compared to the initially percolating network of nanowires in the
absence of the breaks. In the example of FIG. 3, low visibility
patterning can be attained by controlling the number of breaks per
nanowire (and the size of the breaks) to within a target region
that yields a sufficiently high sheet resistance for high
electrical contrast while maintaining a sufficiently small change
in haze for low optical contrast.
[0207] FIG. 4 illustrates an example schematic of metallic
nanowires, here silver nanowires (or AgNWs), subjected to a
chopping or cleaving mechanism or action, in which the nanowires
are severed at one or more locations along their lengths. Without
wishing to be bound by a particular theory, certain chemical agents
can act by preferentially or selectively degrading silver nanowires
at locations including a silver halide, such as silver chloride or
silver bromide, which is included in the silver nanowires as
synthesized. For example, silver nanowires, or other
silver-containing nanostructures or microstructures, can include a
weight percentage of a halide, such as in the form of chlorine or
bromine, in the range of about 0.05% to about 20%, such as from
about 0.05% to about 15%, from about 0.05% to about 10%, from about
0.05% to about 5%, from about 0.05% to about 4%, from about 0.05%
to about 3%, from about 0.05% to about 2%, from about 0.1% to about
20%, from about 0.1% to about 15%, from about 0.1% to about 10%,
from about 0.1% to about 5%, from about 0.1% to about 4%, from
about 0.1% to about 3%, from about 0.1% to about 2%, from about 1%
to about 20%, from about 1% to about 15%, from about 1% to about
10%, from about 1% to about 5%, from about 1% to about 4%, from
about 1% to about 3%, from about 1% to about 2%, from about 5% to
about 20%, from about 5% to about 15%, from about 5% to about 10%,
about 10% to about 20%, from about 10% to about 15%, or from about
15% to about 20%. Certain chemical agents can act as ligands that
solubilize a silver halide included in the silver nanowires by
forming complexes with silver ion, thereby severing the silver
nanowires at locations including the silver halide. Alternatively,
or in combination, certain chemical agents can act by
preferentially or selectively degrading the silver nanowires at
locations including another oxidized form of silver, such as silver
oxide (or Ag.sub.2O) or silver sulfide, or at defects,
dislocations, or other locations along the silver nanowires.
[0208] FIG. 5 illustrates an example schematic of metallic
nanowires, here silver nanowires (or AgNWs), subjected to a
chopping or cleaving mechanism or action, in which junctions
between the nanowires are preferentially or selectively degraded to
sever the nanowires at the junctions and to remove silver from the
junctions, along with a migration or re-deposition of silver onto
intact or severed nanowires adjacent to the junctions. Without
wishing to be bound by a particular theory, certain chemical agents
can act by preferentially or selectively degrading silver nanowires
at locations including a silver halide, such as silver chloride or
silver bromide, which is included in the silver nanowires as
synthesized, although the cleaving mechanism also can include
degradation of the silver nanowires at locations including another
oxidized form of silver, such as silver oxide (or Ag.sub.2O) or
silver sulfide, or at defects, dislocations, or other locations
along the silver nanowires. Certain chemical agents can act as
ligands that solubilize a silver halide included in the silver
nanowires by forming complexes with silver ion, thereby severing
the silver nanowires at locations including the silver halide; in
combination, the same or additional chemical agents can act as
reductants that reduce silver ion in the complexes to yield a
migration or re-deposition of silver. This migration or
re-deposition of silver can increase haze to at least partially
offset haze reduction that results from the removal of silver from
the junctions, and can result in at least some severed or intact
nanowires having larger diameters at their end portions or along
other portions of their lengths, as compared to their original
diameters prior to percolation-inhibiting treatment.
[0209] FIG. 6 illustrates an example schematic of metallic
nanowires, here silver nanowires (or AgNWs), subjected to a
chopping or cleaving mechanism or action, in which junctions
between the nanowires are preferentially or selectively degraded to
sever the nanowires at the junctions and to remove silver from the
junctions, along with a migration or re-deposition of silver as
silver nanoparticles (or AgNPs) or other silver-containing
nanostructures at the junctions. This migration or re-deposition of
silver also can occur elsewhere beyond the junctions. Without
wishing to be bound by a particular theory, certain chemical agents
can act by preferentially or selectively degrading silver nanowires
at locations including a silver halide, such as silver chloride or
silver bromide, which is included in the silver nanowires as
synthesized, although the cleaving mechanism also can include
degradation of the silver nanowires at locations including another
oxidized form of silver, such as silver oxide (or Ag.sub.2O) or
silver sulfide, or at defects, dislocations, or other locations
along the silver nanowires. Certain chemical agents can act as
ligands that solubilize a silver halide included in the silver
nanowires by forming complexes with silver ion, thereby severing
the silver nanowires at locations including the silver halide; in
combination, the same or additional chemical agents can act as
reductants that reduce silver ion in the complexes to yield a
migration or re-deposition of silver as silver nanoparticles. This
migration or re-deposition of silver can increase haze to at least
partially offset haze reduction that results from the removal of
silver from the junctions.
[0210] Combinations of two or more of the foregoing cleaving
mechanisms can be attained in some embodiments. For example,
nanowires can be severed at one or more locations along their
lengths, along with a migration or re-deposition of silver onto
intact or severed nanowires as well as a migration or re-deposition
of silver as silver nanoparticles or other silver-containing
nanostructures.
[0211] By subjecting conductive structures to balanced or partial
degradation according to a cleaving mechanism, low visibility
patterning can be attained. For example, a surface area coverage
(e.g., expressed as a percentage) of conductive structures in lower
conductance portions can be less than, or no greater than, a
corresponding surface area coverage of conductive structures in
higher conductance portions, but the surface area coverage of the
conductive structures in the lower conductance portions can be
maintained to within at least about 5% of the surface area coverage
of the conductive structures in the higher conductance portions,
such as at least about 10%, at least about 13%, at least about 15%,
at least about 17%, at least about 20%, at least about 23%, at
least about 25%, at least about 27%, at least about 30%, at least
about 33%, at least about 35%, at least about 37%, at least about
40%, at least about 43%, at least about 45%, at least about 47%, at
least about 50%, at least about 53%, at least about 55%, at least
about 57%, at least about 60%, at least about 63%, at least about
65%, at least about 67%, at least about 70%, at least about 73%, at
least about 75%, at least about 77%, or at least about 80%, and up
to about 85%, up to about 87%, up to about 90%, up to about 93%, up
to about 95%, or more. Surface area coverage can be based on image
analysis of one or more images, such as one or more scanning
electron microscopy (or SEM) images, with an area occupied by
conductive structures in an image corresponding to pixels having
brightness or other intensity values at or above a threshold value
(or at or below a threshold value in other implementations), and
can be calculated relative to an area sample size of, for example,
at least about 200 .mu.m.times.about 200 .mu.m, at least about 250
.mu.m.times.about 250 .mu.m, or at least about 500
.mu.m.times.about 500 .mu.m.
[0212] As another example, a loading level of an electrically
conductive or semiconducting material, such as silver or another
metal in the case of metallic nanowires, in lower conductance
portions can be less than, or no greater than, a corresponding
loading level of the electrically conductive or semiconducting
material in higher conductance portions, but the loading level in
the lower conductance portions can be maintained to within at least
about 5% of the loading level in the higher conductance portions,
such as at least about 10%, at least about 13%, at least about 15%,
at least about 17%, at least about 20%, at least about 23%, at
least about 25%, at least about 27%, at least about 30%, at least
about 33%, at least about 35%, at least about 37%, at least about
40%, at least about 43%, at least about 45%, at least about 47%, at
least about 50%, at least about 53%, at least about 55%, at least
about 57%, at least about 60%, at least about 63%, at least about
65%, at least about 67%, at least about 70%, at least about 73%, at
least about 75%, at least about 77%, or at least about 80%, and up
to about 85%, up to about 87%, up to about 90%, up to about 93%, up
to about 95%, or more. Loading levels can be expressed in terms of
weight of an electrically conductive or semiconducting material per
unit area, and can be derived based on input coating solution and
method parameters (e.g., a material loading in solution, a solution
injection rate, or a coated wet thickness), microscopic analysis
(e.g., by scanning electron microscopy, atomic force microscopy, or
other techniques), or spectroscopic analysis, such as Rutherford
backscattering spectroscopy.
[0213] As another example, among nanowires in higher and lower
conductance portions, an average, a median, or a mode length of
nanowires in the lower conductance portions can be less than an
average, a median, or a mode length of nanowires in the higher
conductance portions, but can be kept within about 1/200 of the
average, median, or mode length of the nanowires in the higher
conductance portions, such as within about 1/150, within about
1/130, within about 1/100, within about 1/70, within about 1/50,
within about 1/45, within about 1/40, within about 1/35, within
about 1/30, within about 1/25, within about 1/20, within about
1/15, within about 1/10, within about 1/9, within about 1/8, within
about 1/7, within about 1/6, within about 1/5, within about 1/4,
within about 1/3, or within about 1/2. For example, an average, a
median, or a mode length of the nanowires in the lower conductance
portions can be less than an average, a median, or a mode length of
the nanowires in the higher conductance portions, but can be kept
in the range of about 1/200 to about 9/10 of the average, median,
or mode length of the nanowires in the higher conductance portions,
such as about 1/200 to about 4/5, about 1/150 to about 4/5, about
1/130 to about 4/5, about 1/100 to about 4/5, about 1/70 to about
4/5, about 1/50 to about 4/5, about 1/45 to about 4/5, about 1/40
to about 4/5, about 1/35 to about 4/5, about 1/30 to about 4/5,
about 1/25 to about 4/5, about 1/20 to about 4/5, about 1/15 to
about 4/5, about 1/10 to about 4/5, about 1/9 to about 4/5, about
1/8 to about 4/5, about 1/7 to about 4/5, about 1/6 to about 4/5,
about 1/5 to about 4/5, about 1/4 to about 4/5, about 1/3 to about
4/5, or about 1/2 to about 4/5. Nanowire lengths can be based on
image analysis of one or more images, such as one or more SEM
images, and can be calculated relative to a sample size of
nanowires in the images of, for example, at least 50 nanowires, at
least 100 nanowires, at least 200 nanowires, or at least 500
nanowires.
[0214] As another example, among nanowires in higher and lower
conductance portions, an average, a median, or a mode aspect ratio
of nanowires in the lower conductance portions can be less than an
average, a median, or a mode aspect ratio of nanowires in the
higher conductance portions, but can be kept within about 1/200 of
the average, median, or mode aspect ratio of the nanowires in the
higher conductance portions, such as within about 1/150, within
about 1/130, within about 1/100, within about 1/70, within about
1/50, within about 1/45, within about 1/40, within about 1/35,
within about 1/30, within about 1/25, within about 1/20, within
about 1/15, within about 1/10, within about 1/9, within about 1/8,
within about 1/7, within about 1/6, within about 1/5, within about
1/4, within about 1/3, or within about 1/2. For example, an
average, a median, or a mode aspect ratio of the nanowires in the
lower conductance portions can be less than an average, a median,
or a mode aspect ratio of the nanowires in the higher conductance
portions, but can be kept in the range of about 1/200 to about 9/10
of the average, median, or mode aspect ratio of the nanowires in
the higher conductance portions, such as about 1/200 to about 4/5,
about 1/150 to about 4/5, about 1/130 to about 4/5, about 1/100 to
about 4/5, about 1/70 to about 4/5, about 1/50 to about 4/5, about
1/45 to about 4/5, about 1/40 to about 4/5, about 1/35 to about
4/5, about 1/30 to about 4/5, about 1/25 to about 4/5, about 1/20
to about 4/5, about 1/15 to about 4/5, about 1/10 to about 4/5,
about 1/9 to about 4/5, about 1/8 to about 4/5, about 1/7 to about
4/5, about 1/6 to about 4/5, about 1/5 to about 4/5, about 1/4 to
about 4/5, about 1/3 to about 4/5, or about 1/2 to about 4/5.
Nanowire aspect ratios can be based on image analysis of one or
more images, such as one or more SEM images, and can be calculated
relative to a sample size of nanowires in the images of, for
example, at least 50 nanowires, at least 100 nanowires, at least
200 nanowires, or at least 500 nanowires.
[0215] As a further example for the case where a cleavage mechanism
involves re-deposition of silver or another material as
nanoparticles, a percentage by number of nanoparticles relative to
all nanostructures in a lower conductance portion can be greater
than a percentage by number of nanoparticles relative to all
nanostructures in a higher conductance portion, such as where the
percentage by number of nanoparticles in the lower conductance
portion is at least about 1.1 times, at least about 1.2 times, at
least about 1.3 times, at least about 1.5 times, at least about 1.7
times, at least about 2 times, at least about 2.5 times, at least
about 3 times, at least about 4 times, at least about 5 times, at
least about 10 times, at least about 15 times, or at least about 20
times the corresponding percentage by number of nanoparticles in
the higher conductance portion, and where the percentage by number
of nanoparticles in the lower conductance portion is at least about
0.3%, at least about 0.5%, at least about 0.7%, at least about 1%,
at least about 2%, at least about 3%, at least about 4%, at least
about 5%, at least about 6%, at least about 7%, at least about 8%,
at least about 9%, at least about 10%, at least about 11%, at least
about 12%, at least about 13%, at least about 14%, at least about
15%, at least about 20%, at least about 25%, or at least about 30%,
and up to about 35%, up to about 40%, up to about 45%, or more.
[0216] In the case of inhibition of percolation through
degradation, suitable chemical agents can include at least one
complexing agent (or ligand), or a combination of at least one
complexing agent and at least one reducing agent (or reductant or
an anti-oxidant).
[0217] In some embodiments for the case of metallic nanowires or
other conductive structures formed of, or including, a metal, a
suitable complexing agent for the metal can solubilize an oxidized
form of the metal, such as an ionic form of the metal as metal
ions, by forming complexes with the metal ions. The oxidized form
of the metal can be included in the conductive structures as
synthesized, can be formed in situ as part of surface embedding or
otherwise incorporating the conductive structures into a host
material, can be formed in situ as part of percolation-inhibition
treatment, such as through action of water or dissolved oxygen, or
a combination of two or more of the foregoing. By solubilizing the
oxidized form of the metal, the complexing agent can dissolve or
sever the conductive structures at locations including the oxidized
form of the metal.
[0218] A suitable complexing agent (designated as L) for a metal
(an ionic form of the metal designated as M, where the metal has an
oxidation state such as 1+, 2+, 3+, and so forth) can drive a
reaction or an equilibrium towards the formation of a metal-ligand
complex (designated as ML), such as according to:
M+L.fwdarw.ML (1)
M+nL.fwdarw.ML.sub.n, n is an integer.gtoreq.2 (2)
where a metal-ligand stability parameter (or constant) can be used
to characterize an extent to which the reactions (1) and (2) are
driven towards the formation of a metal-ligand complex and, hence,
a strength of binding or affinity of the complexing agent for the
metal, and, in the case of reaction (1), the metal-ligand stability
parameter can be designated as K.sub.1=[ML]/[M][L], and, in the
case of reaction (2), the metal-ligand stability parameter can be
designated as .beta..sub.n=[ML.sub.n]/[M][L].sup.n. Values for
metal-ligand stability parameters and associated test conditions
can be obtained from, for example, the International Union of Pure
and Applied Chemistry (or IUPAC) Stability Constants Database,
available from Academic Software. For example, where M is Ag.sup.+,
thiosulfate has a value for log.sub.10K.sub.1 of about 9.47 and a
value for log.sub.10.beta..sub.2 of about 13.15,
ethylenediaminetetraacetic acid has a value for log.sub.10K.sub.1
of about 7.3, thiocyanate has a value for log.sub.10K.sub.1 of
about 3.64 and a value for log.sub.10.beta..sub.2 of about 5.56,
ethylenediamine has a value for log.sub.10K.sub.1 of about 5.05 and
a value for log.sub.10.beta..sub.2 of about 11.12, chloride has a
value for log.sub.10K.sub.1 of about 3.23 and a value for
log.sub.10.beta..sub.2 of about 5.15, and ammonia has a value for
log.sub.10K.sub.1 of about 3.22 and a value for
log.sub.10.beta..sub.2 of about 7.21. More generally, and with
respect to the metal M, suitable complexing agents of some
embodiments can have at least one, or both, of log.sub.10K.sub.1
and log.sub.10.beta..sub.2 greater than 1, such as at least or
greater than about 2, at least about 2.5, at least about 3, at
least about 3.5, at least about 4, at least about 4.5, at least
about 5, at least about 5.5, or at least about 6. In embodiments in
which a complexing agent is used in combination with a reducing
agent, selection of the complexing agent can involve a balance
between sufficient strength of binding or affinity of the
complexing agent for a metal without excessive or largely
irreversible binding or affinity for the metal that would impede a
reduction function of the reducing agent. In such embodiments,
suitable complexing agents can have log.sub.10K.sub.1 within the
above-stated ranges but no greater than about 9.4, such as no
greater than about 9, no greater than about 8.5, no greater than
about 8, no greater than about 7.5, or no greater than about 7, and
can have log.sub.10.beta..sub.2 within the above-stated ranges but
no greater than about 13, such as no greater than about 12.5 or no
greater than about 12.
[0219] Examples of suitable chemical agents that can act as
complexing agents (or as sources of complexing agents or ligands)
include Group 15 element-containing (e.g., nitrogen-containing)
compounds or Lewis bases, and can be in the form of small
molecules, monomers, oligomers, and polymers that are terminated,
derivatized, or substituted with one or more types of Group 15
element-containing functional groups or that include one or more
Group 15 element atoms or Group 15 element-containing groups, such
as in backbone structures of oligomers or polymers. Examples of
suitable Group 15 element-containing compounds include organic and
inorganic amines, such as ammonia, primary organic amines (cyclic
or acyclic, unsaturated or saturated) and polyamines (linear,
branched, or dendritic), secondary organic amines (cyclic or
acyclic, unsaturated or saturated) and polyamines (linear,
branched, or dendritic), and tertiary organic amines (cyclic or
acyclic, unsaturated or saturated) and polyamines (linear,
branched, or dendritic), such as polylysine, aziridine,
aziridine-based compounds, derivatized aziridine-based compounds,
polyethylenimine (linear, branched, or dendritic), and phosphorus,
arsenic, antimony, and bismuth analogues of the foregoing compounds
as well as derivatized versions of the foregoing compounds.
[0220] Examples of suitable amines include those having the
formula: N(R)(R')(R'') where R, R' and R'' are independently
selected from hydride groups, alkyl groups, alkenyl groups, alkynyl
groups, aryl groups, other unsaturated or saturated, linear or
branched hydrocarbon groups (e.g., hydrocarbon groups including
from 1-20, 1-15, 1-10, 1-8, or 1-5 carbon atoms), poly(alkylene
oxide) groups, siloxane or polysiloxane groups, and derivatives
thereof. Phosphorus, arsenic, antimony, and bismuth analogues of
the foregoing compounds are also contemplated, such as where
nitrogen is replaced by phosphorus, arsenic, antimony, or
bismuth.
[0221] Examples of suitable polyamines include those having the
formula:
R.sub.2N((C.sub.nR.sub.2n).sub.xNR).sub.a(C.sub.mR.sub.2m).sub.yNR.sub.2,
where R is a hydride group, an alkyl group, an alkenyl group, an
alkynyl group, an aryl group, another unsaturated or saturated,
linear or branched hydrocarbon group (e.g., hydrocarbon groups
including from 1-20, 1-15, 1-10, 1-8, or 1-5 carbon atoms), a
poly(alkylene oxide) group, a siloxane or a polysiloxane group, or
a derivative thereof, and n, m, x, y, a are integers each
independently .gtoreq.0 or .gtoreq.1 (e.g., 0 or more, 1 or more, 2
or more, 3 or more, 4 or more, 5 or more, or 6 or more). The
formula also can be generalized as
RR'N((C.sub.nR''.sub.2n).sub.xNR''').sub.a(C.sub.nR''''.sub.2m).sub.yNR''-
'''R'''''', where the various R groups are independently selected
from hydride groups, alkyl groups, alkenyl groups, alkynyl groups,
aryl groups, other unsaturated or saturated, linear or branched
hydrocarbon groups (e.g., hydrocarbon groups including from 1-20,
1-15, 1-10, 1-8, or 1-5 carbon atoms), poly(alkylene oxide) groups,
siloxane or polysiloxane groups, and derivatives thereof, and n, m,
x, y, a are integers each independently .gtoreq.0 or .gtoreq.1
(e.g., 0 or more, 1 or more, 2 or more, 3 or more, 4 or more, 5 or
more, or 6 or more). Additional examples of suitable polyamines
include those having the formula:
RR'N--[(R'').sub.x--NR'''--(R'''').sub.y].sub.z--NR'''''R'''''',
where the R, R', R''', R''''', and R'''''' groups are independently
selected from hydride groups, alkyl groups, alkenyl groups, alkynyl
groups, aryl groups, other unsaturated or saturated, linear or
branched hydrocarbon groups (e.g., hydrocarbon groups including
from 1-20, 1-15, 1-10, 1-8, or 1-5 carbon atoms), poly(alkylene
oxide) groups, siloxane or polysiloxane groups, and derivatives
thereof, and the R'' and R'''' groups are independently selected
from alkylene groups (e.g., methylene or --CH.sub.2-- and ethylene
or --CH.sub.2--CH.sub.2--), alkenylene groups, alkynylene groups,
arylene groups, other unsaturated or saturated, linear or branched
hydrocarbon groups (e.g., hydrocarbon groups including from 1-20,
1-15, 1-10, 1-8, or 1-5 carbon atoms), poly(alkylene oxide) groups,
siloxane or polysiloxane groups, and derivatives thereof, and x, y,
z are integers each independently .gtoreq.0 or .gtoreq.1 (e.g., 0
or more, 1 or more, 2 or more, 3 or more, 4 or more, 5 or more, or
6 or more). Phosphorus, arsenic, antimony, and bismuth analogues of
the foregoing compounds are also contemplated, such as where at
least one nitrogen in the foregoing formulas are replaced by
phosphorus, arsenic, antimony, or bismuth.
[0222] Additional examples of suitable polyamines and Group 15
element analogues of polyamines include those having the
formula:
##STR00002##
where R.sub.1, R.sub.2, R.sub.3, and S are independently selected
from hydride groups, alkyl groups, alkenyl groups, alkynyl groups,
aryl groups, other unsaturated or saturated, linear or branched
hydrocarbon groups (e.g., hydrocarbon groups including from 1-20,
1-15, 1-10, 1-8, or 1-5 carbon atoms), poly(alkylene oxide) groups,
siloxane or polysiloxane groups, and derivatives thereof, L is
selected from alkylene groups, alkenylene groups, alkynylene
groups, arylene groups, other unsaturated or saturated, linear or
branched hydrocarbon groups (e.g., hydrocarbon groups including
from 1-20, 1-15, 1-10, 1-8, or 1-5 carbon atoms), poly(alkylene
oxide) groups, siloxane or polysiloxane groups, and derivatives
thereof, A and B are independently selected from nitrogen,
phosphorus, arsenic, antimony, and bismuth, and n is an
integer.gtoreq.0 or .gtoreq.1 (e.g., 0 or more, 1 or more, 2 or
more, 3 or more, 4 or more, 5 or more, or 6 or more), and where for
n>1:
[0223] L in different ones of the n units can be the same or
different, and are independently selected from alkylene groups,
alkenylene groups, alkynylene groups, arylene groups, other
unsaturated or saturated, linear or branched hydrocarbon groups,
poly(alkylene oxide) groups, siloxane or polysiloxane groups, and
derivatives thereof,
[0224] S in different ones of the n units can be the same or
different, and are independently selected from hydride groups,
alkyl groups, alkenyl groups, alkynyl groups, aryl groups, other
unsaturated or saturated, linear or branched hydrocarbon groups,
poly(alkylene oxide) groups, siloxane or polysiloxane groups, and
derivatives thereof, and
[0225] B in different ones of the n units can be the same or
different, and are independently selected from nitrogen,
phosphorus, arsenic, antimony, and bismuth.
[0226] Specific examples of amines and polyamines include ammonia,
bis(hexamethylene)triamine (or
H.sub.2N--(CH.sub.2).sub.6--NH--(CH.sub.2).sub.6--NH.sub.2),
ethylenediamine (or H.sub.2N--(CH.sub.2).sub.2--NH.sub.2),
diethylenetriamine (or
H.sub.2N--(CH.sub.2).sub.2--NH--(CH.sub.2).sub.2--NH.sub.2),
octylamine (or CH.sub.3--(CH.sub.2).sub.7--NH.sub.2), decylamine
(or CH.sub.3--(CH.sub.2).sub.9--NH.sub.2), triethylenetetraamine
(or
H.sub.2N--(CH.sub.2).sub.2--NH--(CH.sub.2).sub.2--NH--(CH.sub.2).sub.2--N-
H.sub.2), N-methylethylenediamine (or
CH.sub.3--NH--(CH.sub.2).sub.2--NH.sub.2),
N,N'-dimethylethylenediamine (or
(CH.sub.3).sub.2N--(CH.sub.2).sub.2--NH.sub.2),
N,N,N'-trimethylethylenediamine (or
CH.sub.3--NH--(CH.sub.2).sub.2--N(CH.sub.3).sub.2),
N,N'-diisopropylethylenediamine (or
(CH.sub.3).sub.2CH--NH--(CH.sub.2).sub.2--N--CH(CH.sub.3).sub.2),
and tetraethylpentaamine (or
H.sub.2N--(CH.sub.2).sub.2--NH--(CH.sub.2).sub.2--NH--(CH.sub.2).sub.2--N-
H--(CH.sub.2).sub.2--NH.sub.2). Other specific examples of amines
and polyamines include ethylenediamine tetraacetic acid, imidazoles
(e.g., di-imidazole and tri-imidazole), pyrimidine, purine,
spermine, urea, lysine, ethanolamine hydrochloride, hydantoin,
thiourea, and amine-oxides (or oxidized amines). Further examples
include aminated polymers, such as poly(vinylamine) and related
copolymers. In some embodiments, suitable amines and polyamines
include those lacking a carboxy group (or lacking a carbonyl group
or lacking --(C.dbd.S)--), or including no more than 2 carboxy
groups per molecule (or no more than 2 carbonyl groups or no more 2
--(C.dbd.S)-- per molecule), or no more than 1 carboxy group per
molecule (or no more than 1 carbonyl group or no more 1
--(C.dbd.S)-- per molecule).
[0227] Additional specific examples of polyamines include
polyethylenimine, which also can be referred as polyaziridine or
poly(iminoethylene). Polyethylenimine can be used in several
molecular weights, can be branched, linear, or dendritic, and can
be used as derivatives, such as polyethylenimine derivatized with
various side chains or functional groups. Suitable molecular
weights for polyethylenimine include about 800 and about 25,000
(number or weight average), although other molecular weights are
contemplated, such as about 100,000 or less, about 50,000 or less,
about 25,000 or less, about 20,000 or less, about 10,000 or less,
about 5,000 or less, or about 1,000 or less, and down to about 500
or less. A suitable concentration of polyethylenimine (or another
chemical agent) in a percolation-inhibition composition can be, for
example, about 1.0 mg/ml, but can be adjusted according to a
coating thickness of the composition that is applied to a
substrate. An amount of polyethylenimine deposited on a surface may
drive a cleaving mechanism or action, such as about 1.0 mg/ml for
about 0.75 mil drawdown bar (about 10 .mu.m wet thickness), and
about 0.2 mg/ml for about 4 mil drawdown bar (about 50 .mu.m wet
thickness). These example amounts correspond to about 10 nm of
polyethylenimine deposited on a surface. More generally for some
embodiments, a loading level of polyethylenimine (or another
chemical agent) can be at least about 1 ng/cm.sup.2 of surface
area, which corresponds to at least about 0.01 nm of
polyethylenimine deposited on the surface (assuming density of
about 1 g/cm.sup.3), such as at least about 10 ng/cm.sup.2 of
surface area, as at least about 50 ng/cm.sup.2 of surface area, as
at least about 100 ng/cm.sup.2 of surface area, or as at least
about 500 ng/cm.sup.2 of surface area. Treatment can include using
multiple passes at lower loading levels, wherein a cumulative
loading level is at least about 1 ng/cm.sup.2 of surface area. It
is contemplated that polyethylenimine can be deposited or otherwise
applied to a surface as monomers, followed by polymerization of the
monomers to form polyethylenimine.
[0228] In terms of low visibility patterning, polyethylenimine is
closely index-matched to various substrates to reduce a change in
haze after treatment, where an index of refraction of
polyethylenimine is about 1.52, an index of refraction of PMMA is
about 1.49, an index of refraction of PET is about 1.57, and an
index of refraction of polycarbonate is about 1.59. More generally
for some embodiments, polyethylenimine (or another chemical agent)
can have an index of refraction that is within .+-.0.3, .+-.0.2,
.+-.0.18, .+-.0.15, .+-.0.13, .+-.0.1, .+-.0.8, or .+-.0.5 of a
polymer or other host material in which conductive structures are
embedded. In other embodiments, a rinsing operation is carried out
to remove polyethylenimine (or another chemical agent) subsequent
to treatment, such that close index-matching is not required.
[0229] Further examples of suitable chemical agents that can act as
complexing agents (or as sources of complexing agents or ligands)
include transition metal or ammonium halides (e.g., silver halides
such as silver chloride or silver bromide), transition metal or
ammonium oxides (e.g., silver oxide), transition metal or ammonium
sulfides (e.g., silver sulfide), other silver (e.g.,
Ag.sup.+)-containing chemical agents, alkali metal (e.g., sodium or
potassium) or ammonium thiocyanates, alkali metal (e.g., sodium or
potassium) or ammonium polysulfides, alkali metal (e.g., sodium or
potassium) sulfides, alkali metal (e.g., sodium or potassium) or
ammonium thiosulfates, alkali metal (e.g., sodium or potassium)
halides (e.g., chloride or bromide), metal or ammonium cyanides,
ammonium carbonate, and ammonium carbamate.
[0230] Certain chemical agents can serve a dual function as a
complexing agent as well as a reducing agent, in which case an
additional or a separate reducing agent can be omitted from a
percolation-inhibition composition of some embodiments. For
example, certain amines and polyamines, such as
bis(hexamethylene)triamine and polyethylenimine, among others
listed above, can serve a dual function as a complexing-reducing
agent. In other embodiments, a reducing agent can be included in
combination with a complexing agent. For example, an alkali metal,
an alkali metal thiocyanate (e.g., sodium thiocyanate), or ammonium
thiocyanate can be used in combination with a reducing agent, such
as hydroquinone, hydroquinone derivatives, ascorbic acid, or
combinations of reducing agents including superadditive mixtures
such as phenidone/hydroquinone mixtures.
[0231] In some embodiments for the case of metallic nanowires or
other conductive structures formed of, or including, a metal, a
suitable reducing agent for the metal can reduce an oxidized form
of the metal, which is bound to a complexing agent, by driving a
reduction of the metal to its elemental form. This reduction of the
metal can yield a migration of the metal away from breaks along the
conductive structures and re-deposition of the metal elsewhere.
[0232] A strength of a reducing agent with respect to reducing a
metal can be characterized in terms of a relative placement of the
reducing agent and the metal in the electrochemical series, with
reducing agents of greater reducing strengths being placed higher
than the metal in the electrochemical series. As will be
understood, the electrochemical series is an arrangement of
materials in order of their electrode potentials (redox
potentials), with the more negative electrode potentials placed at
the top of the electrochemical series, and the more positive
electrode potentials placed at the bottom. Electrode potentials can
be specified relative a reference electrode, and, in the case of
the standard hydrogen electrode, electrode potentials are referred
to as standard electrode potentials. A material that is higher in
the electrochemical series can be more readily oxidized than a
material lower in the electrochemical series and thus is effective
as a reducing agent, while a material that is lower in the
electrochemical series can be more readily reduced than a material
higher in the electrochemical series and thus is effective as an
oxidizing agent. With respect to reducing a metal, suitable
reducing agents of some embodiments can have a more negative
electrode potential than the metal, and a difference (e.g., an
absolute difference) in electrode potentials of a reducing agent
and the metal can be at least about 0.1 Volts, such as at least
about 0.2 Volts, at least about 0.3 Volts, at least about 0.4
Volts, at least about 0.5 Volts, at least about 0.7 Volts, at least
about 1 Volts, at least about 1.3 Volts, or at least about 1.5
Volts, and up to about 1.7 Volts, up to about 2 Volts, or more.
[0233] Examples of suitable chemical agents that can act as
reducing agents (or as sources of reducing agents or reductants)
include inorganic compounds, such as sodium borohydride, and
organic compounds, such as citrates, amines and polyamines (e.g.,
phenidone, 4-(methylamino)phenol sulfate (or metol), and others
listed above as suitable complexing agents), aldehydes (e.g.,
gluteraldehyde or formaldehyde), sulfites, and alcohols (e.g.,
polyols, hydroquinone, hydroquinone derivatives, such as
hydroquinone with substituents like 2-hydroxy or tetramethyl,
ascorbic acid, others listed above as suitable embedding and
carrier fluids), and derivatives and combinations of the
foregoing.
[0234] As explained above for some embodiments in the case of
metallic nanowires or other conductive structures formed of, or
including, a metal, an oxidized form of the metal can be included
in the conductive structures as synthesized or can be formed in
situ, in which case an oxidizing agent can be omitted from a
percolation-inhibition composition of some embodiments. Further,
the omission of an oxidizing agent can mitigate against excessive
oxidation of the conductive structures, which can result in
excessive degradation of the conductive structures and undesired
optical contrast of treated and untreated portions of a patterned
transparent conductor. It will be understood that the omission of
an oxidizing agent can encompass an absence of any oxidizing agent
in an absolute sense, but need not necessarily refer to such
absolute sense. Rather, a percolation-inhibition composition that
omits or is devoid of an oxidizing agent more generally can
encompass a sufficiently small or a trace amount of the oxidizing
agent, such that an amount of any oxidizing agent (e.g., expressed
in terms of a concentration (weight or moles per unit volume) or a
weight or volume percentage relative to a total weight or volume)
in the percolation-inhibition composition relative to an amount of
a complexing agent in the percolation-inhibition composition is no
greater than about 1/20, no greater than about 1/30, no greater
than about 1/40, no greater than about 1/50, no greater than about
1/100, no greater than about 1/500, or no greater than about
1/1,000, or such that the amount of any oxidizing agent in the
percolation-inhibition composition relative to an amount of a
reducing agent in the percolation-inhibition composition is no
greater than about 1/20, no greater than about 1/30, no greater
than about 1/40, no greater than about 1/50, no greater than about
1/100, no greater than about 1/500, or no greater than about
1/1,000. Thus, for example, a percolation-inhibition composition
that omits or is devoid of an oxidizing agent can encompass
un-intentional contaminants or impurities, such as environmental
oxygen or moisture or low level impurities.
[0235] It should be understood that environmental oxygen,
environmental moisture, other environmental contaminants or
impurities, and combinations thereof may affect an oxidation state
of a metal included in surfaces of conductive structures. As such,
control of environmental contaminant level (e.g., by treatment in a
water-free or oxygen-free or reduced water or reduced oxygen
environment) can be used to control or modify the effect of a
percolation-inhibition composition. In particular, certain
complexing agents act solely or preferentially on an oxidized form
of a metal (e.g., sodium thiocyanate complexes readily with Ag+ in
AgCl or Ag.sub.2O, but is substantially inert to elemental silver
or Ag(0)). For example, removal of substantially all environmental
oxygen and dissolved oxygen in the percolation-inhibition
composition can reduce the rate or extent of
percolation-inhibition.
[0236] In other embodiments, an oxidizing agent can be included in
a percolation-inhibition composition. Examples of suitable
oxidizing agents include inorganic peroxides, such as hydrogen
peroxide and ammonium peroxide; organic peroxides, such as benzoyl
peroxide, 2-butanone peroxide, cumene hydroperoxide, and alkoyl
peroxides like lauryl peroxide; inorganic and organic hypohalites
(e.g., hypochlorites), inorganic and organic acids, inorganic and
organic persulfates, organic complexes of iron (III), potassium
iodate, ferric nitrate, and other etchants. Oxidation also can be
accomplished by ozone or ultraviolet-ozone treatment.
[0237] Inhibition of percolation through degradation can be
accomplished in other manners, such as through sulfidation.
Sulfidation can be accomplished by one or more of organic and
inorganic sulfides (e.g., hydrogen sulfide, sodium sulfide, and
others), Group 16 analogs of organic and inorganic sulfides (e.g.,
selenides and tellurides), and other sulfidizing agents. Surface
modification of conductive structures can be accomplished by one or
more of surface alloying and galvanic treatments to form layers or
shells of a metal or a metal alloy of lower electrical conductivity
at least partially surrounding the structures.
[0238] One or more degradation chemical agents can be dispersed in
a suitable composition, which can include a thickener (or a
viscosity modifier) and a solvent or other carrier fluid, and the
composition can be applied in a substantially uniform manner or in
a spatially selective or varying manner. A complexing agent can be
included in a percolation-inhibition composition in an amount of at
least about 0.01 wt. %, such as at least about 0.05 wt. %, at least
about 0.1 wt. %, at least about 0.5 wt. %, at least about 1 wt. %,
at least about 2 wt. %, at least about 3 wt. %, at least about 4
wt. %, or at least about 5 wt. %, and up to about 10 wt. %, up to
about 15 wt. %, up to about 20 wt. %, or more, and, in some
embodiments, even up to about 90%, up to about 95%, or up to about
100 wt. %. In embodiments where two or more complexing agents are
included in a percolation-inhibition composition, a combined amount
of the complexing agents can be within the above-stated ranges. In
embodiments where a reducing agent is included in a
percolation-inhibition composition in combination with a complexing
agent, an amount of the reducing agent can be at least about 0.01
wt. %, such as at least about 0.05 wt. %, at least about 0.1 wt. %,
at least about 0.5 wt. %, at least about 1 wt. %, at least about 2
wt. %, at least about 3 wt. %, at least about 4 wt. %, or at least
about 5 wt. %, and up to about 10 wt. %, up to about 15 wt. %, up
to about 20 wt. %, or more. In embodiments where two or more
reducing agents are included in a percolation-inhibition
composition, a combined amount of the reducing agents can be within
the above-stated ranges. In some embodiments, an amount of a
reducing agent (e.g., in terms of wt. %) in a
percolation-inhibition composition can be no greater than, or less
than, an amount of a complexing agent in the percolation-inhibition
composition, although a greater relative amount of a reducing agent
is contemplated for other embodiments.
[0239] In some embodiments, a suitable solvent is one that is
substantially inert towards a polymer or other material included in
a transparent conductor to be treated, so as to mitigate against
undesired degradation of the transparent conductor through
solubilizing the polymer. Examples of suitable solvents include
water and alcohols, among others listed above as suitable carrier
fluids. Thus, for example, a percolation-inhibition composition of
some embodiments can be water-based or can be an aqueous
composition. For such embodiments, degradation chemical agents and
other components of the aqueous composition should be sufficiently
water-soluble or miscible, such as having a solubility, at room
temperature, of at least about 0.5 g, at least about 1 g, at least
about 1.1 g, at least about 1.5 g, at least about 2 g, at least
about 2.5 g, at least about 3 g, at least about 3.5 g, at least
about 4 g, at least about 4.5 g, at least about 5 g, at least about
10 g, at least about 15 g, or at least about 20 g, per 100 g of
water. Similar ranges of solubility can be applicable for an
alcohol or another solvent that is used in place of water.
Solubility of degradation chemical agents and other components in
water or another solvent can also facilitate their removal
subsequent to percolation-inhibition treatment, through a rinsing
operation using water or another solvent. Suitable solvents can
also be pH-adjusted, such as with potassium hydroxide or acetic
acid, in order to alter or improve the functionality of the overall
composition.
[0240] Examples of suitable thickeners include polymer binders,
including water-soluble polymer binders such as
poly(vinylpyrrolidone), polyvinyl alcohol, poly(vinyl
alcohol-co-vinylamine), ethylene-vinyl alcohol copolymer, sodium
polyacrylate, and carbohydrates, such as water-soluble cellulose
derivatives like methylcellulose, hydroxyethylcellulose, and sodium
carboxymethylcellulose, and water-soluble natural polymers like
starch, starch paste, soluble starch, and dextrin. Polystyrene also
can be a suitable thickener. In some embodiments, an amount of a
polymer binder in a percolation-inhibition composition can be in
the range of about 0.01 wt. % to about 50 wt. %, such as about 0.1
wt. % to about 45 wt. %, about 1 wt. % to about 40 wt. %, about 5
wt. % to about 40 wt. %, about 10 wt. % to about 40 wt. %, about 10
wt. % to about 35 wt. %, or about 15 wt. % to about 35 wt. %,
although a polymer binder can be omitted for other embodiments. A
percolation-inhibition composition also can include one or more of
a humectant, a defoamer (or an anti-foaming agent), a surfactant
(or a wetting agent), a rheological filler (e.g., a clay such as
bentonite or other solid filler such as barium sulfate), a pH
modifier, and an anti-colorant (or anti-yellowing agent).
[0241] Suitable degradation chemical agents of some embodiments can
have a low volatility to mitigate against evaporation of the
chemical agents during treatment away from portions intended to
become lower conductance portions and adversely affecting portions
intended to become higher conductance portions. For example,
suitable complexing agents, such as amines and polyamines, can have
a boiling point, at 1 atmosphere, of at least about 80.degree. C.,
at least about 90.degree. C., at least about 100.degree. C., at
least about 110.degree. C., at least about 120.degree. C., at least
about 130.degree. C., at least about 140.degree. C., at least about
150.degree. C., at least about 160.degree. C., at least about
170.degree. C., or at least about 180.degree. C., and up to about
220.degree. C., up to about 240.degree. C., or more. In other
embodiments, a gas phase or otherwise volatile (low boiling point)
degradation chemical agent (either, or both, a complexing agent and
a reducing agent) can be used, for example, if portions of a
substrate are covered by a protective mask, and unprotected
portions are treated by exposure to volatile chemical agents. In
this case, a solvent may or may not be included. The substrate can
optionally be cooled to below a boiling point of the volatile
chemical agents in order to condense the volatile agents onto the
substrate. Additionally, in embodiments where a
percolation-inhibition composition is patterned directly onto a
substrate, such as via screen printing or other printing methods,
it may be desirable for a complexing agent and, optionally, a
reducing agent to have low volatility, through the selection of
chemical agents which are non-volatile salts or otherwise have low
volatility (e.g., solids or semi-solids at room temperature). Low
volatility or non-volatile complexing agents can have a specific
advantage that they are less likely to spread to areas of a
substrate which are to remain untreated. The phenomenon of unwanted
spread of a percolation-inhibition composition beyond an intended
treatment area can be referred to as "overkill," and can be
significantly mitigated or eliminated by careful selection of one
or more of a low volatility (e.g., boiling point above about
100.degree. C.) complexing agent, appropriate activation
temperature (e.g., below the boiling point of the complexing
agent), and appropriate treatment time.
[0242] Additionally, in other embodiments, metal ion sources can be
added to, or included in, a percolation-inhibition composition in
order to further facilitate or control a loading level of a metal
(e.g., silver) remaining on a substrate after treatment. Suitable
metal ion sources can include, for example, silver nitrate, silver
lactate, tetrachloroauric acid, palladium nitrate, silver acetate,
palladium chloride, gold ethylene diamine complex, and other
metal-containing salts or metal-ligand complexes. A metal ion
source can be added to a composition in the range of about 0.0001
wt. % to about 5 wt. %. The metal ion source can be a source of the
same metal as a metal of a percolating network, or can be a source
of a different metal.
[0243] Sequential deposition of components of a
percolation-inhibition composition can also be practiced in some
embodiments. For example, a conductive structure-containing
substrate can be treated with a metal complexing agent in one
process operation, the complexing agent can then be removed from a
surface of the substrate in another process operation, and the
surface can be treated with a reducing agent in a further process
operation, optionally in the presence of a metal ion source.
[0244] In some embodiments, a solvent may not be necessary for the
function of a percolation-inhibition composition. For example,
certain metal complexing agents can be melted or otherwise
deposited onto a substrate surface and can inhibit percolation in
their native state.
[0245] An electrical conductivity of a percolating network of
conductive structures can be reduced by applying any combination of
the above methods--physical, chemical, and degradation, by applying
the appropriate chemical agents or treatments as described above to
the network of conductive structures, before or after percolation
is achieved, either sequentially or simultaneously.
[0246] FIG. 7 through FIG. 9 illustrate manufacturing methods of
patterned transparent conductors, according to embodiments of this
disclosure. As shown in FIG. 7A, a substrate 302 is provided, and
conductive structures 300 are at least partially embedded into a
surface of the substrate 302. As shown in FIG. 7B, a bottom layer
304 is provided, a coating or a top layer 306 is applied on top of
the bottom layer 304, and conductive structures 300 are at least
partially embedded into a surface of the coating 306. As shown in
FIG. 7C, a bottom layer 304 is provided, conductive structures 300
are applied on top of the bottom layer 304, and an over-coating or
a top layer 308 is applied on top of the bottom layer 304 and at
least partially surrounding the structures 300.
[0247] Next, a percolation-inhibiting treatment is applied in a
spatially selective or varying manner as shown in FIG. 8A through
FIG. 8C. For example, a percolation-inhibiting composition can be
applied in a pattern through printing, such as screen, ink-jet,
aerosol-jet, flexographic, ultrasonic spray, continuous deposition,
slot die, doctor bar, patch, gravure, intaglio, pad, roll, offset,
mimeography, or imprint. The percolation-inhibiting composition can
be adjusted to aid in printing, such as a relatively high viscosity
(e.g., greater than about 100 centipoise, such as at least about
200, about 300, about 400, about 500, or about 600 centipoise) with
shear thinning behavior in the case of screen printing, and a
relatively low viscosity in the case of ink jetprinting. In the
case of the over-coated implementation of FIG. 8C, a thickness of
the over-coating 308 can be adjusted as relatively thin to aid in
exposing the structures 300 to the percolation-inhibiting
composition, the over-coating 308 can be formed of, or can include,
a host material sufficiently permeable to, or is otherwise
sufficiently susceptible to, the percolation-inhibiting composition
to allow permeation of the composition into the over-coating 308,
or both. Portions exposed to the percolation-inhibiting composition
form lower conductance portions 312 as shown in FIG. 9A through
FIG. 9C, while portions not exposed to the percolation-inhibiting
composition remain electrically conductive, forming higher
conductance portions 310 as shown in FIG. 9A through FIG. 9C.
Optionally, an activating or annealing operation can be carried out
to promote reaction or other activity of the percolation-inhibiting
composition, such as through application of heat or other thermal
or energizing treatment at a temperature above room temperature or
above about 25.degree. C., at least about 30.degree. C., at least
about 40.degree. C., at least about 50.degree. C., at least about
60.degree. C., at least about 70.degree. C., or at least about
80.degree. C., and up to about 200.degree. C., up to about
150.degree. C., up to about 140.degree. C., up to about 130.degree.
C., up to about 120.degree. C., up to about 110.degree. C., or up
to about 100.degree. C., and for a duration of at least about 1
minute, at least about 2 minutes, at least about 3 minutes, at
least about 4 minutes, or at least about 5 minutes, and up to about
2 hours, up to about 1.5 hour, up to about 1 hour, up to about 50
minutes, up to about 45 minutes, up to about 40 minutes, or up to
about 35 minutes. The activation operation can include, for
example, thermal treatment (e.g., an oven), exposure to ultraviolet
light, flash annealing, exposure to electron beam, or chemical
activation. The percolation-inhibiting composition can be viewed as
an "active" mask, since it actively performs the function of
inhibiting percolation in the portions exposed to the "active"
mask. Optionally, a cleaning, washing, or rinsing operation can be
carried out to remove any remaining percolation-inhibiting
composition, such as through the use of pressurized water or other
suitable solvents, and a quenching operation can be carried out to
quench further reaction or other activity of the
percolation-inhibiting composition.
[0248] For applications in which low visibility patterning is
desired, the percolation-inhibiting composition can have the effect
of degrading or reducing electrical conductivity of the structures
300 in the lower conductance portions 312, while maintaining
optical characteristics (e.g., haze, transmittance, reflectance,
absorbance, luster, and color) of the lower conductance portions
312 as sufficiently matching optical characteristics of the higher
conductance portions 310. In cases where inhibition of percolation
affects or alters one or more optical properties, the
percolation-inhibiting composition can include optical matching
additives that can compensate for the alteration in the one or more
optical properties. Examples of optical matching additives include
nanoparticles or other fillers formed of insulating or lower
conductivity materials, liquid crystal materials, and photochromic
materials (e.g., silver halides for glass substrates or organic
photochromic molecules such as oxazines, or naphthopyrans for
polymer substrates). Optical matching additives can be surface
embedded through the inclusion of a suitable embedding fluid in the
percolation-inhibiting composition.
[0249] FIG. 10 through FIG. 14 illustrate manufacturing methods of
patterned transparent conductors, according to embodiments of this
disclosure. As shown in FIG. 10A, a substrate 402 is provided, and
conductive structures 400 are at least partially embedded into a
surface of the substrate 402. As shown in FIG. 10B, a bottom layer
404 is provided, a coating or a top layer 406 is applied on top of
the bottom layer 404, and conductive structures 400 are at least
partially embedded into a surface of the coating 406. As shown in
FIG. 10C, a bottom layer 404 is provided, conductive structures 400
are applied on top of the bottom layer 404, and an over-coating or
a top layer 408 is applied on top of the bottom layer 404 and at
least partially surrounding the structures 400.
[0250] Next, a physical mask, a patterned photoresist layer, a
particulate-based mask (e.g., silica or titania), or other type of
"passive" mask 414 having a low permeability for a
percolation-inhibiting composition can be placed or applied on top
of the devices as shown in FIG. 11A through FIG. 11C. The mask 414
can be viewed as a "passive" mask, since it performs a passive,
protective function instead of actively affecting percolation. The
mask 414 has a pattern that covers selected portions of the devices
while leaving other portions uncovered or exposed.
[0251] Next, as shown in FIG. 12A through FIG. 12C, a
percolation-inhibiting treatment is applied in a substantially
uniform manner, such as by applying a percolation-inhibiting
composition through the use of a coating process or tool (e.g., dip
coating), spraying, or other low viscosity, solution-phase
application method. The inclusion of the mask 414 results in
spatially selective or varying application of the
percolation-inhibiting composition through gaps or openings in the
mask 414. In the case of the over-coated implementation of FIG.
12C, a thickness of the over-coating 408 can be adjusted as
relatively thin to aid in exposing the structures 400 to the
percolation-inhibiting composition, the over-coating 408 can be
formed of, or can include, a host material sufficiently permeable
to, or is otherwise sufficiently susceptible to, the
percolation-inhibiting composition to allow permeation of the
composition into the over-coating 408, or both. Portions exposed to
the percolation-inhibiting composition (and are not covered by the
mask 414) form lower conductance portions 410, while portions not
exposed to the percolation-inhibiting composition (and are covered
by the mask 414) remain conductive, forming higher conductance
portions 412. Optionally, an activating or annealing operation can
be carried out to promote reaction or other activity of the
percolation-inhibiting composition, such as through application of
heat or other thermal or energizing treatment at a temperature
above room temperature or above about 25.degree. C., at least about
30.degree. C., at least about 40.degree. C., at least about
50.degree. C., at least about 60.degree. C., at least about
70.degree. C., or at least about 80.degree. C., and up to about
150.degree. C., up to about 140.degree. C., up to about 130.degree.
C., up to about 120.degree. C., up to about 110.degree. C., or up
to about 100.degree. C., and for a duration of at least about 1
minute, at least about 2 minutes, at least about 3 minutes, at
least about 4 minutes, or at least about 5 minutes, and up to about
2 hours, up to about 1.5 hour, up to about 1 hour, up to about 50
minutes, up to about 45 minutes, up to about 40 minutes, or up to
about 35 minutes. Optionally, a cleaning, washing, or rinsing
operation can be carried out to remove any remaining
percolation-inhibiting composition, such as through the use of
pressurized water or other suitable solvents, and a quenching
operation can be carried out to quench further reaction or other
activity of the percolation-inhibiting composition.
[0252] For applications in which low visibility patterning is
desired, the percolation-inhibiting composition can have the effect
of degrading or reducing electrical conductivity of the structures
400 in the lower conductance portions 410, while maintaining
optical characteristics (e.g., haze, transmittance, reflectance,
absorbance, luster, and color) of the lower conductance portions
410 as sufficiently matching optical characteristics of the higher
conductance portions 412. In cases where inhibition of percolation
affects or alters one or more optical properties, the
percolation-inhibiting composition can include optical matching
additives that can compensate for the alteration in the one or more
optical properties. Optical matching additives can be surface
embedded through the inclusion of a suitable embedding fluid in the
percolation-inhibiting composition.
[0253] As shown in FIG. 13A through FIG. 13C, the mask 414 can be
removed, such as by dissolving the mask or other suitable physical
or chemical treatment. Alternatively, as shown in FIG. 14A through
FIG. 14C, the mask 414 can be retained. For applications in which
low visibility patterning is desired, a planarization coating or
layer 416 can be applied on top of the devices as shown in FIG. 14A
through FIG. 14C, so as to planarize the resulting devices as an
aid to lamination or formation of additional layers over the
devices, and so that optical characteristics (e.g., haze,
transmittance, reflectance, absorbance, luster, and color) of the
lower conductance portions 410 (not covered by the mask 414)
sufficiently match optical characteristics of the higher
conductance portions 412 (covered by the mask 414). As shown in
FIG. 14A through FIG. 14C, the planarization layer 416 is applied
to cover both the lower conductance portions 410 (not covered by
the mask 414) and the higher conductance portions 412 (covered by
the mask 414); in other embodiments, the planarization layer 416
can be applied to selectively cover the lower conductance portions
410 (not covered by the mask 414). For example, the planarization
layer 416 can be formed of, or can include, an optically clear
adhesive or other polymer, optionally including optical matching
additives to compensate for the presence of the mask 414 over the
higher conductance portions 412. To reduce visibility of the mask
414, a refractive index of the mask 414 can sufficiently match that
of the planarization layer 416. In some embodiments, a difference
between the refractive indices of the mask 414 and the
planarization layer 416 (e.g., an absolute difference between the
values expressed as a percentage relative to either of the values)
can be no greater than about 10%, such as no greater than about 5%,
no greater than about 4%, no greater than about 3%, no greater than
about 2%, no greater than about 1%, or no greater than about 0.5%,
and down to about 0.1%, down to about 0.01%, down to about 0.001%,
or less. Also, the planarization layer 416 can be sufficiently thin
to reduce additional effects related to either, or both, haze and
color. In some embodiments, a thickness of the planarization layer
416 can be no greater than about 5 times a thickness of the mask
414, such as no greater than about 4.5 times, no greater than about
4 times, no greater than about 3.5 times, no greater than about 3
times, no greater than about 2.5 times, no greater than about 2
times, no greater than about 1.5 times, no greater than about 1.4
times, no greater than about 1.3 times, no greater than about 1.2
times, or no greater than about 1.1 times.
[0254] In other embodiments, an optically clear adhesive or other
index matching material can be used to reduce or hide surface
roughness differences between treated and untreated portions of a
substrate as patterned or otherwise treated with a
percolation-inhibition composition. These surface roughness
differences may arise due to one or more of the following list,
which are provided by way of example: residues from surfactants,
polymer binders, solid fillers, or other percolation-inhibition
composition components; preferential effect of a
percolation-inhibition composition on an exposed metal (e.g.,
exposed silver nanowires or portions thereof affected more than
embedded silver nanowires or portions thereof); and interaction of
a percolation-inhibition composition with a treated substrate
surface.
[0255] Other embodiments of manufacturing methods of patterned
transparent conductors are contemplated. For example, in some
embodiments, a percolation-inhibition composition is applied
substantially uniformly over a network of conductive structures,
and an activating operation can be carried out in a spatially
selective or varying manner, such as by heating or otherwise
energizing the network of conductive structures in a spatially
localized or varying manner to cause the percolation-inhibition
composition to act locally to form lower conductance portions.
Energizing can be provided by electromagnetic radiation, such as by
a laser, thermally, such as by contact with a heated patterned
stamp, or a combination of the foregoing.
Devices Including Transparent Conductors
[0256] The transparent conductors described herein can be used as
transparent conductive electrodes in a variety of devices. Examples
of suitable devices include solar cells (e.g., thin-film solar
cells and crystalline silicon solar cells), display devices (e.g.,
flat panel displays, liquid crystal displays (or LCDs), plasma
displays, organic light emitting diode (or OLED) displays,
electronic-paper (or e-paper), quantum dot displays (e.g., QLED
Displays), and flexible displays), solid-state lighting devices
(e.g., OLED lighting devices), touch sensor devices (e.g.,
projected capacitive touch sensor devices, touch-on-glass sensor
devices, touch-on-lens projected capacitive touch sensor devices,
on-cell or in-cell projected capacitive touch sensor devices, self
capacitive touch sensor devices, surface capacitive touch sensor
devices, and resistive touch sensor devices), smart windows (or
other windows), windshields, aerospace transparencies,
electromagnetic interference shields, charge dissipation shields,
and anti-static shields, as well as other electronic, optical,
optoelectronic, quantum, photovoltaic, and plasmonic devices. The
transparent conductors can be tuned or optimized depending on the
particular application, such as work function matching in the
context of photovoltaic devices or tuning of the transparent
conductors to form Ohmic contacts with other device components or
layers.
[0257] In some embodiments, the transparent conductors can be used
as electrodes in touch sensor devices. A touch sensor device is
typically implemented as an interactive input device integrated
with a display, which allows a user to provide inputs by contacting
a touch screen. The touch screen is typically transparent to allow
light and images to transmit through the device.
[0258] FIG. 15 illustrates an example of a projected capacitive
touch sensor device 2400 according to an embodiment of this
disclosure. The touch sensor device 2400 includes a thin-film
separator 2404 that is disposed between a pair of patterned
transparent conductive electrodes 2402 and 2406, as well as a rigid
touch screen 2408 that is disposed adjacent to a top surface of the
transparent conductive electrode 2406. A change in capacitance
occurs when a user contacts the touch screen 2408, and a controller
(not illustrated) senses the change and resolves a coordinate of
the user contact. Advantageously, either, or both, of the
transparent conductive electrodes 2402 and 2406 can be implemented
using the transparent conductors described herein. It is also
contemplated that the transparent conductors can be included in
resistive touch sensor devices (e.g., 4-wire, 5-wire, and 8-wire
resistive touch sensor devices), which include a flexible touch
screen and operate based on electrical contact between a pair of
transparent conductive electrodes when a user presses the flexible
touch screen.
EXAMPLES
[0259] The following examples describe specific aspects of some
embodiments of this disclosure to illustrate and provide a
description for those of ordinary skill in the art. The examples
should not be construed as limiting this disclosure, as the
examples merely provide specific methodology useful in
understanding and practicing some embodiments of this
disclosure.
Example 1
[0260] A network of silver nanowires embedded in a surface of a
polycarbonate (or PC) film is formed by draw down coating of a
silver nanowire dispersion, containing silver nanowires, a carrier
solvent, and an embedding solvent, on a sheet of PC. An electrical
conductivity of the dried film is about 100 .OMEGA./sq when
measured by a non-contact, eddy current-based sheet resistance
measurement device, such as a Napson EC-80P, after thermal
treatment of the film at about 100.degree. C. for about 20 minutes.
A solution of about 40 wt. % 2-mercapto ethanol, about 20 wt. %
isopropyl alcohol (or IPA), and about 40 wt. % methyl isobutyl
ketone (or MIBK) is applied to the pre-heat treated film by doctor
bar with a gap set at about 25-100 .mu.m. After drying the film and
thermal treatment at about 100.degree. C. for about 20 minutes, the
measured OPS is off-scale using the sheet resistance measurement
device (the Napson EC-80P reaches off-scale measurement at 1,300
OPS, but further measurement shows that the OPS is well above 1,300
OPS), indicating that the nanowire network is rendered
non-percolating. Optical microscopy reveals no visible damage to
the nanowires.
Example 2
[0261] A network of silver nanowires embedded in a surface of a
poly(methyl methacrylate) (or PMMA) film coated at about 1 .mu.m
thickness on a poly(ethylene terephthalate) (or PET) layer is
formed by draw down coating of a silver nanowire dispersion,
containing silver nanowires, a carrier solvent, and an embedding
solvent, on a sheet of the PMMA-coated PET. An electrical
conductivity of the dried film is about 100 .OMEGA./sq when measure
by a non-contact, eddy current-based sheet resistance measurement
device, such as a Napson EC-80P, after thermal treatment of the
film at about 100.degree. C. for about 20 minutes. After this
thermal treatment, a solution of polyethylenimine in IPA is applied
to the film using a doctor bar with a gap of about 25 .mu.m. After
a further thermal treatment at about 100.degree. C. for about 20
minutes, the film is rendered insulating as measured by an
off-scale Napson EC-80P reading (the Napson EC-80P reaches
off-scale measurement at 1,300 OPS, but further measurement shows
that the OPS is well above 1,300 OPS). Optical microscopy reveals
that the silver nanowires are severed along their lengths during
the further thermal treatment, by the action of the
polyethylenimine.
Example 3
[0262] A network of silver nanowires embedded in a surface of a
PMMA film coated at about 1 .mu.m thickness on a PET layer is
formed by draw down coating of a silver nanowire dispersion,
containing silver nanowires, a carrier solvent, and an embedding
solvent, on a sheet of the PMMA-coated PET. An electrical
conductivity of the dried film is about 100 .OMEGA./sq when
measured by a non-contact, eddy current-based sheet resistance
measurement device, such as a Napson EC-80P, after thermal
treatment of the film at about 100.degree. C. for about 20 minutes.
A solution of 2-butanone peroxide in IPA is applied to the pre-heat
treated film by doctor bar with a gap set at about 25-100 .mu.m.
After drying the film and thermal treatment at about 100.degree. C.
for about 20 minutes, the measured OPS is off-scale using the sheet
resistance measurement device (the Napson EC-80P reaches off-scale
measurement at 1,300 OPS, but further measurement shows that the
OPS is well above 1,300 OPS), indicating that the nanowire network
is rendered non-percolating. Optical microscopy reveals that the
silver nanowires are etched or partially etched by the action of
the organic peroxide.
Example 4
[0263] FIG. 16 is a scanning electron microscopy (or SEM) image of
a network of silver nanowires embedded in a substrate, without or
prior to application of an electrical conductivity modifying agent.
FIG. 17 is a SEM image of a silver nanowire-embedded substrate
subsequent to application of hydrogen peroxide. As can be observed,
silver nanowires are largely removed or degraded, with some
silver-containing material remaining in the substrate. In this
case, the treated portion of the substrate is readily distinguished
from an untreated portion by the human eye.
[0264] By comparison, FIG. 18 is a SEM image of a silver
nanowire-embedded substrate subsequent to application of ammonia.
As can be observed, silver nanowires are severed along their
lengths. Without wishing to be bound by a particular theory,
ammonia can act by preferentially or selectively degrading silver
nanowires at locations including silver halide, which is included
in the silver nanowires as synthesized.
[0265] Also by comparison, FIG. 19 is a SEM image of a silver
nanowire-embedded substrate subsequent to application of
polyethylenimine. As can be observed, junctions between silver
nanowires are preferentially or selectively degraded to sever
silver nanowires at the junctions and to remove silver from the
junctions, along with a migration or re-deposition of silver onto
intact or severed silver nanowires adjacent to the junctions.
[0266] Also by comparison, FIG. 20 is a SEM image of a silver
nanowire-embedded substrate subsequent to application of
bis(hexamethylene)triamine. As can be observed, junctions between
silver nanowires are preferentially or selectively degraded to
sever silver nanowires at the junctions and to remove silver from
the junctions, along with a migration or re-deposition of silver as
silver nanoparticles at the junctions, although a final morphology
can be affected or varied by composition and processing
parameters.
Example 5
[0267] To evaluate the role of a silver halide in the activity of
an electrical conductivity modifying agent, silver nanowires
containing different amounts of a silver halide, here silver
chloride, are embedded in substrates, and the silver-nanowire
embedded substrates are treated with bis(hexamethylene)triamine
FIG. 21A is a SEM image of a substrate embedded with silver
nanowires containing about 0.6 wt. % of silver chloride, subsequent
to application of bis(hexamethylene)triamine, and FIG. 21B is a SEM
image of a substrate embedded with silver nanowires containing
about 3.41 wt. % of silver chloride, subsequent to application of
bis(hexamethylene)triamine. As can be observed, a greater number of
nanowire breaks is evident for silver nanowires containing a
greater amount of silver chloride.
Example 6
[0268] Various amines were tested by drop-casting onto a
spin-coated network of silver nanowires on silicon and activating
by annealing at about 100.degree. C. for about 15 minutes.
[0269] In the case of diethylenetriamine (or DETA), FIG. 22 (top
panel) is a SEM image of silver nanowires treated with 100 vol. %
DETA, and FIG. 22 (bottom panel) is a SEM image of silver nanowires
treated with 50 vol. % DETA in IPA. As can be observed, silver
nanowires are largely converted to nanoparticles when using 100
vol. % DETA after activation, while use of 50 vol. % DETA results
in nanowire breaks and a migration or re-deposition of silver onto
severed silver nanowires.
[0270] FIG. 23 is a SEM image of silver nanowires treated with
octylamine. As can be observed, junctions between silver nanowires
are preferentially or selectively degraded to sever silver
nanowires at the junctions and to remove silver from the junctions,
along with a migration or re-deposition of silver as silver
nanoparticles at the junctions and a migration or re-deposition of
silver onto severed silver nanowires.
[0271] FIG. 24 is a SEM image of silver nanowires treated with
decylamine. As can be observed, junctions between silver nanowires
are preferentially or selectively degraded to sever silver
nanowires at the junctions and to remove silver from the junctions,
along with a migration or re-deposition of silver as silver
nanoparticles at the junctions and a migration or re-deposition of
silver onto severed silver nanowires.
[0272] FIG. 25 is a SEM image of silver nanowires treated with
triethylenetetramine. As can be observed, silver nanowires are
severed to remove silver, along with a migration or re-deposition
of silver.
[0273] FIG. 26 (top panel) is a SEM image of silver nanowires
treated with N-methylethylenediamine, and FIG. 26 (bottom panel) is
a magnified view of the image. As can be observed, junctions
between silver nanowires are preferentially or selectively degraded
to sever silver nanowires at the junctions and to remove silver
from the junctions, along with a migration or re-deposition of
silver as silver nanoparticles at the junctions as well as
elsewhere beyond the junctions.
[0274] FIG. 27 is a SEM image of silver nanowires treated with
N,N'-dimethylethylenediamine. As can be observed, junctions between
silver nanowires are preferentially or selectively degraded to
sever silver nanowires at the junctions and to remove silver from
the junctions, along with a migration or re-deposition of silver as
silver nanoparticles at the junctions.
[0275] FIG. 28 is a SEM image of silver nanowires treated with
N,N'-diisopropylethylenediamine. As can be observed, silver
nanowires are severed along their lengths.
Example 7
[0276] FIG. 29 is a SEM image of silver nanowires treated with
sodium thiosulfate. As can be observed, silver nanowires are
severed along their lengths.
Example 8
[0277] To demonstrate the ability to render a network of silver
nanowires insulating while reducing changes in surface area
coverage and haze for low optical contrast, samples treated with
bis(hexamethylene)triamine and sodium thiosulfate were evaluated
relative to untreated samples.
[0278] FIG. 30 is a SEM image of untreated silver nanowires, FIG.
31 is a SEM image of silver nanowires treated with
bis(hexamethylene)triamine, and FIG. 32 is a SEM image of silver
nanowires treated with sodium thiosulfate. As can be observed,
treated silver nanowires are severed along their lengths,
effectively rendering a network of the silver nanowires to be
non-percolating.
[0279] Measurements of surface area coverage, haze, and electrical
conductivity are performed for the treated and untreated samples,
and results are set forth below, where values for surface area
coverage are derived over an area of 250 .mu.m.times.250 nm.
TABLE-US-00001 Bis(hexamethylene) Surface area triamine coverage
Haze Ohms per square Untreated 7.4% 1.35% 91 treated 3.1% 1.22%
Off-scale
TABLE-US-00002 Surface area Sodium thiosulfate coverage Haze Ohms
per square untreated 7.9% 1.33% 164 treated 4.2% 1.15%
Off-scale
Example 9
[0280] To evaluate the impact of an electrical conductivity
modifying agent on lengths of silver nanowires, measurements of
lengths were performed from SEM images of a sample of a patterned
transparent conductor. The measurements were performed for 100
silver nanowires in an untreated (or unpatterned) region and 100
silver nanowires in a treated (or patterned) region. Results are
set forth in FIG. 33. As a result of breaks along lengths of silver
nanowires, an average length of treated silver nanowires is reduced
to about 2.4 .mu.m, from about 10.5 .mu.m for untreated silver
nanowires. Also, a 30.sup.th percentile length shifts from less
than about 9 .mu.m for untreated silver nanowires to less than
about 1 .mu.m for treated silver nanowires.
Example 10
[0281] Percolation-inhibition compositions are prepared with
components and amounts as follows:
[0282] (1) about 15 wt. % of a polymer binder as a viscosity
modifier (poly(vinylalcohol-co-vinylamine)), about 0.15 wt. % of an
oil-based defoamer (available as Rhodoline.RTM. 646), about 1 wt. %
of an electrical conductivity modifying agent
(bis(hexamethylene)triamine), and balance de-ionized (or DI)
water.
[0283] (2) about 18 wt. % of a polymer binder as a viscosity
modifier (poly(vinylalcohol-co-vinylamine)), about 0.15 wt. % of an
oil-based defoamer (available as Rhodoline.RTM. 646), about 10 wt.
% of a humectant (glycerol), about 2.5 wt. % of an electrical
conductivity modifying agent (polyethyleneimine), and balance DI
water.
[0284] (3) about 14.98 wt. % of a polymer binder as a viscosity
modifier (poly(vinylalcohol-co-vinylamine)), about 0.15 wt. % of an
oil-based defoamer (available as Rhodoline.RTM. 646), about 20 wt.
% of a humectant (triacetin), about 0.1 wt. % of a non-ionic
fluorosurfactant (available as Capstone.RTM. FS-35), about 10 wt. %
of an electrical conductivity modifying agent
(bis(hexamethylene)triamine), and balance DI water.
[0285] (4) about 23.14 wt. % of a polymer binder as a viscosity
modifier (poly(vinylalcohol-co-vinylamine)), about 0.15 wt. % of an
oil-based defoamer (available as Rhodoline.RTM. 646), about 10 wt.
% of a humectant (D-sorbitol), about 5 wt. % of an electrical
conductivity modifying agent (triethylenetetramine), and balance DI
water.
[0286] (5) about 21.25 wt. % of a polymer binder as a viscosity
modifier (poly(vinylalcohol-co-vinylamine)), about 0.15 wt. % of an
oil-based defoamer (available as Rhodoline.RTM. 646), about 0.1 wt.
% of a non-ionic fluorosurfactant (available as Capstone.RTM.
FS-35), about 5 wt. % of an electrical conductivity modifying agent
(bis(hexamethylene)triamine), and balance DI water.
Example 11
[0287] A series of percolation-inhibition compositions are prepared
and are composed of about 5 wt. % sodium thiocyanate, and 0 wt. %,
about 0.1 wt. %, about 0.5 wt. %, about 1 wt. %, about 5 wt. %, and
about 10 wt. % ascorbic acid each in DI water. Each composition is
pipetted into a separate vial, and the vials are capped. The capped
vials are then placed in an oven at about 80.degree. C. for about
45 minutes to equilibrate. The vials are removed from the oven. An
about 1''.times.1'' square of film composed of silver nanowires
embedded into a PMMA top layer on a PET bottom layer is placed into
each vial. The film-containing vials are then incubated for about
60 minutes at about 80.degree. C. in an oven. The films are then
removed from the vials, rinsed with DI water, and dried prior to
measurement and characterization.
[0288] All compositions, including the control sample with 0 wt. %
ascorbic acid, show sheet resistance increase from about 100 OPS
prior to treatment to over about 800,000 OPS after treatment with
the percolation-inhibition composition for points as measured by an
automated 4-point probe sheet resistance mapping tool.
[0289] Optical and scanning electron microscopy analysis of the
treated films show the following observations:
TABLE-US-00003 Ascorbic Acid wt. % Microscopy Observation 0
Chopping of silver nanowires without observable re-deposition of
silver, significant loss of silver from surface (see FIG. 34) 0.1
Fewer chops of silver nanowires and increased re-deposition of
silver versus 0 wt. % ascorbic acid composition (see FIG. 35) 0.5
Fewer chops of silver nanowires and increased re-deposition of
silver versus 0.1 wt. % ascorbic acid composition (see FIG. 36) 1
Fewer chops of silver nanowires and increased re-deposition of
silver versus 0.5 wt. % ascorbic acid composition (see FIG. 37) 5
Fewer chops of silver nanowires and increased re-deposition of
silver versus 1 wt. % ascorbic acid composition (see FIG. 38) 10
Chopping is barely visible, most closely resembles untreated film
(see FIG. 39)
Example 12
[0290] A percolation-inhibition composition composed of about 5 wt.
% bis(hexamethylene)triamine, about 0.1 wt. % silver nitrate, and
DI water is pipetted into a vial and equilibrated at room
temperature. An about 1''.times.1'' square of film composed of
silver nanowires embedded into a PMMA top layer on a PET bottom
layer is then placed into the vial. The vial is incubated at about
80.degree. C. for about 60 minutes in an oven prior to removal from
the oven. The film is then removed from the vial, rinsed with DI
water, dried, measured, and analyzed. The film sheet resistance is
increased, and silver re-deposition on the film can be increased
versus a control sample without silver nitrate.
Example 13
[0291] A percolation-inhibition composition composed of about 100
wt. % bis(hexamethylene)triamine is placed on a film composed of
silver nanowires embedded into a PMMA top layer on a PET bottom
layer. The bis(hexamethylene)triamine powder is sprinkled and
spread onto a portion of the film surface. The film is then placed
in an oven at about 80.degree. C. for about 60 minutes. The
bis(hexamethylene)triamine is observed to melt. After removal from
the oven, the film is washed in DI water to remove excess
bis(hexamethylene)triamine. Optical microscopy and sheet resistance
measurement demonstrate that the sheet resistance of the treated
film portion (and nearby portions due to volatility of
bis(hexamethylene)triamine) is increased significantly, and silver
nanowires are chopped. Some silver appeared to be re-deposited as
nanoparticles on the film.
[0292] A practitioner of ordinary skill in the art may find some
helpful guidance in implementing certain embodiments in U.S. patent
application Ser. No. 13/594,758, filed on Aug. 24, 2012 (published
as US 2013/0056244 on Mar. 7, 2013), the disclosure of which is
incorporated herein by reference in its entirety.
[0293] While this disclosure has been described with reference to
the specific embodiments thereof, it should be understood by those
skilled in the art that various changes may be made and equivalents
may be substituted without departing from the true spirit and scope
of this disclosure as defined by the appended claims. In addition,
many modifications may be made to adapt a particular situation,
material, composition of matter, method, or process to the
objective, spirit and scope of this disclosure. All such
modifications are intended to be within the scope of the claims
appended hereto. In particular, while the methods disclosed herein
have been described with reference to particular operations
performed in a particular order, it will be understood that these
operations may be combined, sub-divided, or re-ordered to form an
equivalent method without departing from the teachings of this
disclosure. Accordingly, unless specifically indicated herein, the
order and grouping of the operations are not limitations of this
disclosure.
* * * * *